ELEMENTARY  GENERAL  SCIENCE 


THE  GUIDE 


ELEMENTARY 
GENERAL  SCIENCE 

WITH   EXPERIMENTS 


BOOK  I. 


BY 

PERCY    E.  ROWELL,  M.  S. 

\\ 

AUTHOR  OF  INTRODUCTION  TO 
GENERAL  SCIENCE 


BERKELEY.  CALIFORNIA 
PERCY  E.  ROWELL 

1914 
ALL  RIGHTS  RESERVED 


TV 


I 


COPYRIGHT,  1913,  1914- 
BY  PERCY  E.  ROWELL 

Published  July.  1913 
Revised  and  reprinted  August,  1914 


MARIN  JOURNAL  PRESS 

SAN  RAFAEL,  CAL.,  U.  S.   A. 


PREFACE. 


This  book,  the  first  of  a  series  of  four,  is  written 
upon  the  basis  that  all  science  must  rest  upon  the  broad 
foundations  of  general  knowledge.  Many  of  the  difficul- 
ties which  have  beset  science  teaching  in  the  grades 
have  been  due  to  the  fact  that  only  a  small  field  of  science 
has  been  taught,  and  that  the  field  has  been  too  minutely 
studied.  To  confine  the  child  of  a  lower  grade  to  a  study 
of  a  single  group  of  phenomena,  just  because  he  is  young, 
is  to  deprive  him  of  natural  opportunities  of  learning. 
There  is  no  reason  why  all  branches  of  science  cannot  be 
learned  by  children,  if  the  beginnings  are  but  presented 
according  to  their  way  of  thinking.  General  knowledge 
is  not  necessarily  superficial. 

The  science  which  is  most  valuable  to  the  child  is 
that  which  explains  the  phenomena  of  the  environment — 
the  science  of  common  things — the  science  of  everyday 
life.  No  one  branch  of  science  can  do  this,  nor  can  any 
one  branch  of  science  be  properly  taught  without  doing  it. 
A  blending  of  all  branches  of  science,  as  a  means  for  the 
best  teaching  of  it  in  the  grades,  is  inevitable. 

The  teaching  of  science  in  the  grades  has  been  handi- 
capped by  the  supposed  necessity  for  elaborate  and  cost- 
Iv  apparatus.  Few  of  the  experiments  in  this  text  require 
even  the  cheaper  apparatus,  while  most  of  them  do  not 
require  anything  which  really  should  be  called  apparatus. 
The  use  of  common  things  to  illustrate  scientific  truths 

357633 


VI  PREFACE 

has  also  the  decided  advantage  of  bringing  the  science 
home  to  the  child.  He  repeats  his  experiments  at  home, 
for  he  has  the  "apparatus",  and  the  science  becomes  his, 
through  the  reproduction. 

The  experiments,  although  very  simple,  do  not 
merely  verify  the  statements  of  the  text,  but  they  elab- 
orate and  add  to  it.  They  are  often  the  source  of 
information,  and  thus  the  pupils  become  imbued  with 
the  desire  for  investigation — the  true  scientific  spirit.  To 
obtain  the  best  results  the  pupils  should  write  up  their 
experiments  in  brief  manner  and  illustrate  their  work 
with  simple  drawings  of  the  apparatus  and  objects  which 
have  been  used. 

There  has  been  no  attempt  at  an  exhaustive  study  o\ 
any  one  thing.  Many  of  the  sections  could  be  enlarged 
to  produce  a  book  in  themselves.  The  attempt  has  been 
made,  however,  to  show  the  balance  which  exists  between 
vegetable  and  animal  life,  and  the  underlying  principles 
which  govern  all  animate  as  well  as  all  inanimate  exist- 
ence. If  the  conditions  are  such  as  to  warrant  the  sne- 
ria.1  and  more  comprehensive  study  of  any  of  the  sec- 
n'ons,  the  List  for  Teachers,  which  the  United  States 
Department  of  Agriculture  has  prepared,  should  be  con- 
sulted. This  list  covers  a  vast  field,  not  alone  from  the 
agricultural  standpoint,  but  from  that  cf  general  science. 

The  work  is  cumulative,  always  building  upon  the  old 
and  constantly  making  use  of  it.  Often  the  foundations 
for  a  section  are  laid  many  sections  before,  and  thus  the 
science  lessons  become  one  whole,  a  complete  blending 
of  the  different  parts  being  accomplished  natnrallv.  and 
without  apparent  effort  on  the  part  of  the  teacher  or 
pupils. 


PREFACE  VII 

Teaching  the  applications  of  science  to  the  industries 
and  the  arts  will  give  the  pupils  the  first  insight  into  their 
own  desires  and  capabilities.  They  will  thus  begin  un- 
consciously to  prepare  themselves  along  the  line  of  pre- 
vocational  work.  Later  they  will  also  realize  the  dignity 
of  labor,  and  the  science  teaching  may  easily  develop  into 
the  various  branches  of  vocational  work,  and  the  pupils 
may  be  given  the  rare  opportunity  of  viewing  the  field  of 
human  endeavor  and  of  truly  choosing  their  career  in  life. 

Many  new  texts  and  other  publications  have  been 
freely  consulted  in  the  preparation  of  this  book.  Since 
much  of  the  material  has  become  common  property, 
specific  acknowledgment  has  not  been  made,  but  the 
author  takes  this  opportunity  of  thanking  the  many  pub- 
lishers who  have  so  kindly  supplied  him  with  reference 
books. 

Especial  thanks  are  due  Mr.  James  B.  Davidson, 
Superintendent  of  Schools  of  Marin  County,  California, 
and  Mr.  David  R.  Jones,  City  Superintendent  of  Schools 
of  San  Rafael,  California,  both  of  whom  have  read  the 
manuscript  and  have  given  to  the  book  the  benefit  of 
their  experience.  Thanks  are  also  due  Messrs  Boggs, 
Davalos,  and  Persell  who  made  many  of  the  drawings. 
Acknowledgement  is  made  through  the  text  for  other 
special  obligations.  The  author  alone  is  responsible  for 
any  mistakes  which  may  have  crept  into  the  work. 

PERCY   ELLIOTT  ROWELL. 
Berkeley,  California. 
Tuly,   1913 


CONTENTS 

Section  Page 

1.  Time  of  Sunrise  and  Sunset       ,         .        ,.    •     .  1 

2.  Experiments         .         .         ,         .        .  1 

3.  Direction.     The  North      V        .        .        .        .«  2 

4.  Circular  Measurement        .        .        .        .        .  7 

5.  Other  Directions         .         .         .         ...  8 

6.  The  Direction  of  Sunrise  and  Sunset        .       ..  10 

7.  Telling  Time  by  the  Sun           .         .   '    '•*'       .  12 

8.  Other  Ways  of    Telling    Time           .<     '.-       .  13 

9.  The  Height  of  the  Sun  at  Noon        *          .        \  15 

10.  The  Light  We  Receive  from  the  Sun       .         .  19 

11.  The  Sunlight  Makes  Plants  Green    ."•'..      .   .\  20 

12.  Other  Changes  of   Color   which    are    Caused   by 

Sunlight         .        .         .       ..        .'        .'.       .  22 

13.  The  Sunlight  Good    for    Plants    and    Animals  25 

14.  Light  Travels  in  Straight  Lines       'if-      *         .  26 

15.  The  Reflection  of  Light              .        .         .         .  29 

16.  Light  from  Sources  Other  Than  the  Sun          .  33 

17.  The  Heat  we  Receive  from  the  Sun         .         .  39 

18.  Expansion  Due  to  Heat  .  .         .44 

19.  The  Thermometer  an  Application  of  Expansion  48 

20.  Heat  Produces  Light          .         .  '      .         .         .  53 

21.  Heat  from   Friction              .         .         .         /       ,  54 

22.  Heat  from  Combustion               .         *        .        .  58 

23.  Combustibles  and  Fuels              .         .         .         .  60 

24.  Flames               ^  .        .        .        .        .        .        .  62 

25.  First  Aid  to  the  Burned              .         .        .     t   .  64 

26.  Conduction  of  Heat  66 


X  CONTENTS 

27.  Air  a  Necessity  of  Life        .         .         ...  71 

28.  Air  in  the  Soil  and  in  Water       .         .         .         .  72 

29.  The  Composition  of  the  Atmophere          .         .  75 

30.  Oxygen  and  its  Uses        '  .         .-        .         .      ..  .1  78 

31.  Nitrogen  and  its  Uses         "...        ..      ..    ...... • '."'1  8.3 

32.  Carbon   Dioxide           ,.         ,        .         .  .     ...        .  81 

33.  Respiration.      The  Necessity  for  Pure  Air        .  85 

34.  Water  is  a  Liquid        .         .....       . .         .  89 

35.  Water  can  Pass  into  Some  Things      .'     •  -.         .  91 

36.  Solution  and  its  Oddities            .      "  .         .         .  95 

37.  Crystals        .         ."         ...         '.         .'   .    .  98 

38.  Water  for  Drinking             .  -      '.     '   .         .         .  100 

39.  Water  for  Cleansing            ...         ;         .      '  .  10? 

40.  Plants  Need  Water            '  .         .-'.-.'  -.        .  105 

41.  Capillarity             .         .         ...;.'.      :  ,'  106 

42.  The  Beginning  of  Plant  Life              .         .         .  113 
4j3.  The  Testing  of  Seeds           .         .'     .._^-r''^~\\4 

44.  The  Proper  Planting  of  Seeds         '  .;        .         .  116 

45.  The  Needs  of  the  Plant      .         ..     .  .        .-     '  I  118 

45.  Birds             .         .         .        .        .     -   .         .        :  120 

47.  Wild  and  Garden  Flowers          .         .         .         ,  122 

48.  Trees             .         .         .         .         .  123 

49.  A  Queer  Plant  — Yeast  ,         .         .         .127 

50.  Another  Queer  Kind  of  Plant— The  Bacteria  129 

51.  Souring  and  Decay      .                                    .         •  130 

52.  Disease  and  Sanitation         . 

53.  The  Source  of  All  Food             ..         *       '' .  •      'V  137 

54.  The  Farm  a  Workshop        .         .        V             . ';  140 

55.  Tilling  the  Soil                  ,    .     .    .         .                  .  HI 

56.  Irrigation  and  Drainage  of  Farms 

57.  Gardening                                        ....  14.i 


CONTENTS  XI 

58.  Simple  Measurement           .         .         .  .  .  151 

59.  Everything  Has  Weight. — The  Balance  .  154 

60.  Everything  Occupies  Space        .         .  .  .  159 

61.  Density         .      .  .       .  .         .         ...  r  .  160 

62.  Drawings              .        .         .      .  .      ,  .   .  "  «.-.  .  162 

63.  Forces                   ..       .        .   ,     .         ,  .  i  .  164 

64.  The  Plumb-bob  and  the  Pendulum  j|  '  .  /  .  167 

65.  The  Lever           .        ...       -.  \    .  .  16S 

66.  The  Inclined   Plane             ,         .         .  "  . '  '  :  .'     170 

67.  The  Lodestone         .    .-...'   ..     •'.  '.>;  .  174 

68.  Steel   Magnets                .        -..        ..        ,  .  .  175 

69.  Weather  Observations       ...      J.  .  .  182 

70.  How  to  Make  Blue-print  Paper       -   .  •'.  .  183 

71.  Solar   Heaters               .         .         .      .   .  .  .  184 

72.  Hot-Air  Engines          .         .         ,       ".  ,  r  185 
73      Fireproofing         .         .         .         .       '.  .   .  i  185 

74.  Waterproofing     ..       .      ...        .        .  .  .  ISO 

75.  Flavoring  Extracts  and  Perfumes      .  .  . .  187 

76.  To  Remove  Grease  Spots  and  Stains  .  .  188 

77.  How  to  Make  Soap            .     -   .         .  ,.  .  188 

78.  Bread    Making             .         ....        •  •  •  l^ 

79.  Alcohol  for  Industrial  Purposes         .  .  .  190 

80.  The  Pantagraph           .         .         .         .  .  .191 

81.  Levelling .192 

APPENDIX. 

Reference  Books  on  Birds      .    .         ...  •  •  195 

Reference  Books  on  Flowers      .         .         .  .  195 

Reference  Books  on  Trees         .       .^         .  .  .  195 

List  of  Apparatus  and  Materials         .         .  :    .  .  196 


LIST  OF  EXPERIMENTS. 

Section  Page 

3.     Expt   1.     To  Locate  the  North  by  the    North 

Star  .     '  .'       .        .  '    ;.        3 

Expt.  2.     The  Movement  of  the  Great  Dipper         4 
Expt.  3.     To  Locate  the  North    by  Means    of 

Shadows  ."        .         .         .         .         5 

5.  Expt.  4.     To  Locate  the  South  by  Means  of  a 

Watch  .         ....         .        8 

6.  Expt.  5.     The  Direction  of  Sunrise  and  Sunset       10 
Expt.  6.     To  Record  the    Direction   of   Sunset      11 

7.  Expt.  7.     The  Sundial         ,        .        ...       .         .12 

8.  Expt.  8.     The  Sand-glass  .         .      ".        •>    '   14 

9.  Expt.  9.     The  Height  of  the  Sun  at  Noon    by 

by  Shadows  .         .         .         .       15 

Expt.   10.     The  Height  of  the  Sun  at  Noon  in 

Degrees  .        .        .        .        .       16 

10.  Expt.  11.     The     Appearance     of     the       Sun 

through  Smoked  Glass  .         .j      19 

11.  Expt.  12.     The  Effect  of  Sunlight  upon  Grow- 

ing Plants     ' 20 

12.  Expt.   13.     Fading  and  Bleaching      .         ...       22 
Expt.  14.     Blue  Prints    of    Leaves    and    other 

Articles  .        .        . ;      .         .       23 

14.  Expt.   15.    The  Way  Light  Travels  .         .       26 
Expt.   16.     How  to  Make  and  Use  a  Pin-hole 

Camera    .         .         .         «         .         .       27 

15.  Expt.   17.     Reflection  from   Mirrors  .         .29 
Expt.   18.     Diffused  Reflection  of  Light    .         .31 


LIST  OF  EXPERIMENTS  XIII 

16.  Expt.  19.     Ordinary  Sources  of  Light      .         .  33 
Expt.  20.     Cold    Light      ..         .         .      -.         .  36 

17.  Expt.  21.     The  Varying  Heat  from  the  Sun    .  40 
Expt.  22.     The  Amount  of  Heat  Received  by 

Different  Colors      .         .        .        .  42 

Expt.  23.     The  "Burning  Glass"       .      -  .  43 

18.  Expt.  24.     Heat  Causes  Expansion           .         .  44 
Expt.  25.     The  Result  of  Unequal  Expansion  46 

19.  Expt.  26.     How  to  Read  a  Thermometer     .•".  50 
Expt.  27.     Hot  or  Cold?            .      V     >':-      •  52 

21.  Expt.  28.     Primitive  Fire-making      .         .        . .  55 
Expt.  29.     The  Flint  and  Steel  Gaslighter         .  56 

22.  Expt.  30.     Complete  and  Incomplete  Combus- 

tion          .        .        .     -,.  .     .        «'  59 

23.  Expt.  31.     The  Combustion  of  Different  Mate- 

rials          ..        .         .      ? :"-:.' •-•'. -I  61 

24.  Expt.  32.     The  Cause  of  Flames      . -.-;,  .      r.j  62 

25.  Expt.  33.     Drill    for    Extinguishing..  Burning 

Clothing           .         .        .      :  .         .  64 

26.  Exot.  34.     Good  and  Poor  Conductors  of  Heat  67 

27.  Expt.  35.     Holding     the     Breath     and     Deep 

Breathing         .        *        .        ,        ;  71 
Expt.  36.     The  Effect  of  Depriving  a  Plant  of 

Air           ....                >  71 

28.  Expt.  37.     To  Show  the  Presence    of  Air    in 

Soil  and  Water        .         .         .         .73 

29.  Expt.  38.     The  Amount  of  Oxygen  in  the  Air  76 
Expt.  39.    The  Amount  of  Carbon  Dioxide  In 

the  Air    . 

30.  Expt.  40.     To  Prepare  and  Use  Oxygen          .  78 
32.     Expt.  41.     Carbon  Dioxide  from   Combustion 

and  the  Breath                                 ' .  82 


XIV  LIST  OF  EXPERIMENTS 

33.  Expt.  42.  The  Capacity  of  the  Lungs      .,       .-  86 

34.  Expt.  43.  The   Level         .        .         .        .        ,  89 
Expt.  44.  Water  Seeks  its  own  Level.       Size 

of  Drops          .'..'-      .        .        .  90 

35.  Expt.  45.  Porous  Bodies  Absorb    Water       .  92 
Expt.  46.  To  Make  Porous  Bodies  Waterproof  93 
Expt.  47.  Filtration           .-     ,  .        .         .         .  93 

36.  Expt.  48.  Solution  and  its  Oddities        ..        .95 
Expt.  49.  The  Use  of  Gasolene  and    Alcohol 

as  Solvents            ".'••-.        .         .  97 

37.  Expt.  50.  Crystallization  .  .         .98 

39.  Expt.  51.  Hard  and  Soft  Water.      Soap          .  103 

40.  Expt.  52.  The  Effect  of  Water    upon    Seeds 

and  Plants                .         .         .         .  106 

41.  Expt.  53.  Examples  of  Capillarity           .      '  ;  107 
Expt.  54.  How  Water  is  Held  in  the  Soil      .  108 
Expt.  55.  Capillarity  in  Plants        ;...-      .         .110 

42.  Expt.  56.  The  "Pocket  Garden"      .                 .  113 

43.  Expt.  57.  Germination    Tests           .        .        .  114 

44.  Expt.  58.  The  Proper  Depth  of  Planting       .  116 

47.  Expt.  59.  A  Flower  Collection        .                 .  122 

48.  Expt.  60.  A  "Tree"  Collection                         .  125 
Expt.  61.  Planting  Tree  Seeds         .                 .  126 

49.  Expt.  62.  Fermentation 

51.     Expt.  63.  How  to  Preserve  Milk      .                 ,  131 

58.  Expt.  64.  Measurement 

59.  Expt.  65.  Making  a  Balance    and    Weighing  156 

60.  Expt.  66.  Displacement  of  Water    by    Solids 

and   Air  . 

61.  Expt.  67.  Density                                                -  161 

62.  Expt.  68.  Blue  Prints  from  Tracings       .         .163 


LIST  OF  EXPERIMENTS  XV 

63.  Expt.  69.  Weighing  by  Elasticity            .  .,  165 

64.  Expt.  70.  The    Pendulum         .....  168 

65.  Expt.  71.  The  Use  of  the  Lever      .     f  .  .'  169 

66.  Expt.  72.  The  Use  of  the  Inclined  Plane  .  170 
68.  Expt.  73.  Magnetic  Materials           .        .  .  175 
68.  Expt.  74.  To  Draw  a  Magnetic  Field      .  .,  176 
68  Expt.  75.  Blue  Prints  of  Magnetic  Fields  .  177 
68.  Expt.  76.  Attraction  and  Repulsion        .  .   .  178 
74.  Expt.  77.  Waterproofing           .         *        .  .  186 
77.  Expt.  78.  Soap  Making    .                 .        .  .  189 
79.  Expt.  79.  Making  and  Distilling  Alcohol  .  191 


THE  GUIDE 


ELEMENTARY  GENERAL  SCIENCE 


THE  SUN,  STARS,  AND  PLANETS. 
1.     Time  of  Sunrise  and  Sunset. 

Did  you  see  the  sun  rise  this  morning?  Was  it  too 
early  for  you?  Does  the  sun  always  rise  before  you  do? 
What  time  did  the  sun  set  last  night?  Does  the  sun 
always  set  at  that  time?  Watch  the  time  of  sunrise  and 
sunset  for  several  days  and  keep  a  record  of  your  results. 

The  days 'are  longer  in  summer  than  in  winter  be- 
cause the  sun  rises  earlier  and  sets  later  than  in  winter. 
The  longest  day  of  the  year  is  June  21  and  the  shortest 
day  is  December  21.  On  two  days  of  the  year  the  sun 
rises  at  six  o'clock  in  the  morning  and  sets  at  six  o'clock 
in  the  evening.  These  two  days  are  half  way  between 
June  21  and  December  21.  Count  the  days  on  a  calendar 
and  tell  what  are  the  dates  of  these  two  days.  These 
days  are  called  the  Equinoxes,  meaning  equal  nights. 

You  will  discover,  if  you  keep  a  record  of  the  time 
of  sunrise  and  sunset,  that  the  sun  always  rises  as  much 
before  noontime  as  it  sets  after  noontime.  See  Experi- 
ment 3.  Thus  the  forenoon  and  the  afternoon  are  of  the 
same  length.  What  can  you  say  of  the  number  of  hours 
between  sunset  and  midnight  and  the  number  of  hours 
between  midnight  and  sunrise? 

2.     Experiments. 

We  can  learn  from  teachers  and  from  books  or  we 


Etem,  Sei.  1 


2  THE  SUN,  STARS,  AND  PLANETS 

can  learn  from  the  things  themselves.  All  of  our  knowl- 
edge comes  from  experience  with  the  actual  things  which 
have  been  studied  in  the  past  by  those  who  have  written 
books  about  them.  The  use  of  books,  then,  saves  time 
for  we  can  read  in  a  few  minutes  the  results  of  years  of 
study.  Our  teachers  also  can  help  us  very  much  because 
they  have  learned  from  other  books,  from  other  teachers, 
and  from  things.  Wherever  it  is  possible  we  should 
study  things.  We  may  forget  what  the  books  say  and 
what  the  teacher  has  said,  but  we  can  easily  remember 
what  we  ourselves  have  done.  W7henever  we  try  to  dis- 
cover from  the  thing  itself  how  it  acts,  we  are  perform- 
ing an  experiment. 

The  best  way  in  which  to  learn  science  is  by  means 
of  experiments,  because  science  is  a  study  of  how  every- 
thing acts  and  why  it  acts  as  it  does.  We  may  not 
have  our  books  with  us  always,  and  if  we  can  discover 
from  the  things  themselves  what  we  want  to  know  we 
shall  become  independent,  and  learn  without  help  from 
books  or  from  teachers.  There  are  many  studies  which 
must  be  learned  from  books  but  science  is  an  exception. 
The  record  which  you  are  keeping  of  the  time  of  sunrise 
and  sunset  is  an  experiment.  The  value  of  experiments, 
then,  is  that  we  can  learn  from  the  very  thing  what  we 
want  to  know. 

3.     Direction.     The  North. 

Sometimes  it  is  important  to  know  in  what  direction 
you  should  go  in  order  to  arrive  at  a  certain  place.  In 
cities  and  towns  the  direction  can  be  easily  learned  from 
the  streets.  We  are  directed  to  go  a  certain  number  of 
blocks  one  way  and  then  a  certain  number  of  blocks  an- 


DIRECTION.     THE  NORTH  3 

other  way.  On  the  ocean  and  in  the  open  country,  how- 
ever, where  there  are  no  roads,  we  must  depend  upon 
some  other  method  of  finding  our  way.  One  method  is 
by  means  of  a  star  which  is  so  nearly  in  the  north  that 
it  is  called  the  North  Star. 

Among  all  the  stars  which  brighten  the  sky  at  night, 
it  would  be  very  hard  to  find  the  North  Star  if  there 
were  not  a  huge  sign  in  the  sky  which  always  points  to 
it.  This  sign  is  called  the  Great  Dipper.  The  two  stars 
which  are  the  farthest  from  the  handle  are  called  the 
''pointers"  because  they  point  to  the  North  Star.  Let  us 
try  to  locate  the  north  by  the  North  Star.  To  do  this 
we  shall  perform  an  experiment. 

Experiment  1.— To  Locate  the  North  by  Means  of 
the  North  Star. 

Materials :     Two  straight  sticks,  string. 

a.  Look  in  the  sky  until  you  find  the  Great  Dipper 
Then  glance  from  one  "pointer"  past  the  other  "pointer" 
until  your  glance  has  gone  beyond  it  five  times  the  dis- 
tance between  the  two  pointers.     There  you  will  see  the 
North  Star.     When  you  look  at  this  star  you  are  looking 
almost  exactly  north. 

b.  If  we  did  not  make  some  record  of  the  direction 
of  the  North  Star  we  should  be  unable  next  day  to    tell 
exactly  where  the  north  is.     To  make  a  record  we  need 
two  sticks.     Drive  one  stick  into  the  ground  in  a  place 
from  which  the  North  Star  is  visible.       Then  go  south 
from  this  stick  about  five  feet  and  drive  the  second  stick 
into  the  ground  in  such  a  position  that  by  looking  just 
past  its  edge,  you  can  see  the  North  Star  just  past  the 
ed<re  of  the  first  stick.     The  two  sticks  are  said  to  be  in 


4  THE  SUN,  STARS,  AND  PLANETS 

line  with  the  North  Star,  because  if  a  line  were  drawn 
from  one  stick  to  the  other,  and  then  extended  far  enough 
it  would  pass  to  the  North  Star.  A  string  stretched  be- 
tween the  two  sticks  forms  a  line  which  points  north. 

Review  Questions,  1. 

1.  When  did  the  sun  rise  this  morning? 

2.  How  can    you    tell    the    time  of  sunrise    by    the 
time  of  sunset? 

3.  Why  are  books  valuable? 

4.  What  is  an  experiment? 

5.  What  are  some  of  the  advantages  of  performing 
experiments? 

6.  When  should   we  use  books  and   when    should 
we  experiment? 

7.  How  do  those  who  write  books  learn   what   to 
write? 

8.  How  do  we  direct  persons  from  one  place  to  an- 
other, in  a  city? 

9.  What  must  we  do  in  the  open  country,  or  on  the 
ocean,  to  know  in  what  direction  we  are  going? 

10.  Why  did  you  drive  two  sticks  in  the  ground  to 
make  a  line  pointing  north?  Could  you  have  done  it 
with  one  stick? 

Experiment  2. — *The  Movement  of  the  Great  Dip- 
per. 

Apparatus:     Rule,  scissors,  dividers. 

Materials:     Cardboard  6"xl2",   paper    fastener,    or 
pin  and  piece  of  cork. 

*  See  Section  62  before  performing  this  experiment 

J 


THE  MOVEMENT  OF  THE  GREAT  DIPPER  5 

a.  Cut  the  cardboard  into  two  squares  6"x6"  and 
find  the  center  of  each  piece.  To  do  this  lay  the  rule 
upon  the  cardboard  so  that  it  crosses  it  and  touches  two 
corners.  Make  a  short  line  near  the  center  and  repeat 
for  the  other  two  corners.  Where  the  two  lines  meet  is 
the  center.  Open  your  dividers  so  that  the  points  are 
two  and  one-half  inches  apart;  place  one  point  upon  the 
center  of  one  piece  of  cardboard  and  draw  a  circle.  Upon 


6  THE  SUN,  STARS,  AND  PLANETS 

this  circle  draw    the    Great    Dipper    and    Cassiopeia,    as 
shown  in  the  illustration,    and  fasten  it  by    means  of    a 
paper  fastener,  or  a  pin  pushed  through  the  centers  into 
a  piece  of  cork. 

b.  Hold  the  apparatus  so  that  you  must  look  toward 
the  north  in  order  to  see  it.     Turn  the  circular  piece  so 
that  the  Great  Dipper  is  in  the  position  in  which  you  saw 
those  stars  at  eight  o'clock  last  night,  and  mark  with  the 
date  the  square  piece  of  cardboard  where  the  line  comes 
which  passes  through  the  "pointers." 

c.  Look  at  the  Great  Dipper  at    seven  o'clock    and 
at  nine  o'clock.     Does  it  move  in  the  same  direction  as 
the  hands  of  a  clock  or  in  the  other  direction? 

d.  Look  at  the  Great  Dipper  once  a  week  for   a  few 
weeks,  and  then  once  a  month,  always  at  eight  o'clock, 
and  mark  the  square  piece  with  the  date.     See  how  much 
of  the  way  around  the  North  Star  the  Great  Dipper  goes 
in  one  month  and  then  tell  where  you  think  the  Great 
Dipper  will  be  in  six  months. 

Experiment  3. — To  Locate  the  North  by  Means  of 
Shadows. 

Apparatus:     Long  nail,  board. 

a.  Drive  the  nail  into  a  level  board  placed  where  the 
sun  will  shine  upon  it  all  day.  Mark  along  the  shadow 
of  the  nail  at  nine,  ten,  and  eleven  o'clock,  in  the  morn- 
ing, and  at  one,  two,  and  three  o'clock  in  the  afternoon. 
Half-way  between  the  shadows  which  were  cast  at  nine 
o'clock  and  three  o'clock  is  north.  Half-way  between 
the  shadows  cast  at  ten  o'clock  and  two  o'clock  also  is 
north.  The  same  is  true  of  the  other  two  shadows.  Can 
you  discover  some  rule  in  regard  to  the  directions  of 


CIRCULAR  MEASUREMENT  7 

shadows  in  the  forenoon  and  in  the  afternoon?  Why  do 
you  think  so  many  shadows  were  marked?  What  would 
you  do  if  part  of  the  day  were  cloudy? 


The  north  side  of  trees  has  the  most  moss,  as  a  rule, 
because  that  side  receives  the  least  sunshine  and  is  the 
wettest.  Since  moss  requires  a  large  amount  of  moisture 
it  cannot  live  on  the  sunny  side  of  trees,  unless  there  is 
a  great  deal  of  rain. 

4.     Circular  Measurement. 

If  you  stand  in  one  place  and  turn  around  until  you 
face  the  same  way  as  you  did  before  you  began  to  move, 
you  have  made  one  revolution,  or  a  complete  circle.  If 
someone  told  you  to  turn  one-half  or  one-quarter  the  way 
around  you  would  know  how  far  to  turn.  Perhaps  you 
could  turn  one-eighth  the  way  around.  If  someone 
wanted  you  to  turn  one-sixteenth  the  way  around  you 
probably  would  not  know  how  far  to  turn.  In  order  to 


8  THE  SUN,  STARS,  AND  PLANETS 

measure  any  part  of  a  revolutionr  or  a  circle,  it  has  been 
divided  into  360  parts  called  degrees.  A  degree  means 
a  step.  The  number  360  was  chosen  because  it  can  be 
divided  evenly  by  so  many  numbers.  See  if  it  can  be 
divided  by  2,  3,  4,  5,  6,  7,  8,  9,  10,  11,  and  12.  Try  divid- 
ing 360  by  other  numbers.  A  semi-circle  divided  into 
180  degrees  is  called  a  protractor.  It  is  used  to  measure 
the  part  of  a  revolution,  or  circle,  which  one  direction 
turns  from  another  direction.  The  short  and  proper  way 
of  writing  "degrees"  is  to  use  a  little  circle  after  the  num- 
ber. For  example,  75  degrees  may  be  written  75°.  This 
means  75  parts  of  a  circle. 

5.     Other  Directions. 

If  you  face  the  north,  the  south  is  behind  you  ;  the 
east  is  at  your  right  and  the  west  is  at  your  left.  These 
four  points  of  direction  are  each  a  quarter  of  a  revolution, 
or  a  quarter  of  a  circle,  from  the  next  one.  How  m^ny 
degrees  between  any  two  of  them?  How  many  degrees 
between  the  north  and  the  south.  If  one  direction  is  181 
dgrees  from  another  direction  the  two  directions  are  said 
to  be  opposite  each  other.  Is  the  east  opposite  to  the 
west?  Why? 

Experiment  4. — To  Locate  the  South  by  Means  of 
*  Watch. 

a.  Hold  the  watch  so  that  the  hour  hand  points 
toward  the  sun.  The  south  direction  will  then  be  just 
half  way  between  the  hour  hand  and  the  figure  XII  on 
the  watch.  Do  this  both  in  the  morning  and  afternoon 
and  see  if  the  result  is  the  same.  Can  you  tell  where  the 
north  is  from  this  experiment? 


OTHER   DIRECTIONS 


These  four  directions,  north,  south,  east,  and   west 

are  not  enough 
for  even  ordinary 
use,  so  the  half- 
way points  are 
named  according 
to  the  directions 
between  which 
they  come.  The 
directions  north 
and  south  are 
named  first,  thus: 
North-east,  north- 
west, south-east, 
and  south  -  west. 
How  many  degrees  are  there  between  north-east  and 
east?  Between  north-east  and  north-west?  Between 
south-east  and  south-west? 

Review  Questions,  2. 

1.  Make  a  drawing  of  the  Great  Dipper  as  it  was 
the  last  time  you  saw  it,  and  write  the  date  and    hour 
when  you  saw  it. 

2.  How  often  does  the  Great  Dipper    seem  to    go 
around  the  North  Star? 

3.  Which  side  of  the  house  is  the  driest,  the  north 
side  or  the  south  side?     Why? 

4.  Is   it  better  to  answer  the    last    question    after 
noticing  the  rooms  of  a  house,  or  to  find  the  answer  in 
some  book? 

5.  How  many  degrees    are  there    in  half    a    circle? 
In  a  quarter  of  a  circle?       If  you  are  walking    along    a 


10  THE  SUN,  STARS,  AND  PLANETS 

street  and  turn  into  a  side  street,  how  many  degrees  do 
you  turn? 

6.  What  is  a  protractor?     For  what  is  it  used? 

7.  If  you  face  the  south,  where  is  the  east?     The 
west  ? 

8.  If  you  are  facing  east,  how  much  must  you  turn 
in  order  to  face  north?     Would  you  turn  toward  the  left 
or  toward  the  right? 

6.     The  Direction  of  Sunrise  and  Sunset 

Where  did  the  sun  rise  this  morning?  Where  did 
it  set  last  night?  Does  the  sun  always  rise  in  the  same 
place?  Does  it  always  set  in  the  same  place?  Where 
would  the  shadow  of  a  stick  point  at  sunrise?  Where  at 
noon?  W^here  at  sunset?  An  experiment  is  the  best 
way  of  answering  these  questions. 

Experiment  5. — *The  Direction  of  Sunrise  and  Sun- 
set by  Shadows. 

Apparatus:     Hatpin,  protractor. 

a.  Stick  a  hatpin  into  the  North-South  line  which 
you  determined  in  Experiment  1,  or  in  Experiment  3. 
Mark  its  shadow  at  sunrise  and  at  sunset.  Place  the 
straight  side  of  the  protractor  along  the  North-South 
line,  with  its  center  mark  at  the  hatpin,  and  tell  how 
many  degrees  the  direction  of  sunrise  is  from  the  North- 
South  line.  Repeat  for  the  direction  of  sunset.  The 
direction  of  sunset  is  as  much  away  from  the  south  direc- 
tion as  is  the  direction  of  sunrise.  See  if  this  is  the  same 
after  a  few  days.  If  this  is  true  we  can  learn  the  di- 
rection of  sunrise  by  knowing  the  direction  of  sunset. 


This  experiment  can  be  performed  only   at   home. 


THE  DIRECTION  OF  SUNRISE 


11 


The  position  of  the  sun  varies  from  day  to  day,  the 
sun  being  farther  to  the  south  in  winter  than  in  sum- 
mer. The  sun  rises  in  the  east  and  sets  in  the  west  on 
two  days  only.  What  are  those  days?  How  can  you 
find  out? 

Experiment  6. — *To  Record  the  Direction  of  Sunset. 

a.  Use  the  apparatus  of  Experiment  5.  and  arrange 
your  results  in  the  form  of  a  table.     Direction  should  al- 
ways be  measured  from  the  North-South  line  whenever 
we  wish  to  be  exact.     If  the  direction  is  just  east  or  just 
west,  we  say  so.     All  other  directions  are  given  as  the 
number  of  degrees  they  are  from  the  north  toward  the 
east  or  west,  and  from  the  south  toward  the  east  or  west. 
If  the  direction  of  sunset  is  80  degrees  from  the  north, 
the  record  should  be:  N.  80°  W.     If  it  is  70  degrees  from 
the  south,  the  record  should  be:  S.  70°  W.     What  is  the 
difference  between  N.  90° W.  and  S.90°  W? 

b.  The  table  for  the  record  should  be  as  follows : 


Date 

Direction 

Once  a  week  is  often  enough  to  take  the  observations. 
Try  it  at  home  and  see  how  your  results  compare  with 
those  of  the  other  pupils. 

Review  Questions-  3. 

1.  Begin    with   the   direction   north,   and   name   the 
four   principal    directions,   and   the    half-way    directions, 
all  the  way  around  the  circle,  starring  toward  the  east 
Now  repeat  starting  toward  the  west. 

2.  Where  did  the  sun  rise  this  morning? 

*  This  experiment  can  be  performed  only  at  home. 


12  THE  SUN,  STARS,  AND  PLANKTS 

3.  How   can  you   tell   the   direction   of   sunrise    by 
knowing  the  direction  of  sunset? 

4.  On   what  days  does  the  sun   rise  at   six  o'clock 
and  set  at  six  o'clock? 

5.  How  can  you  tell  when  it  is  noon  by  a  shadow? 

6.  How  can  you  tell  where  the  north  is  by  a  shadow? 

7.  If  the  sun  sets  S.  85°  W.  where    does  it    rise? 
Make  a  drawing  of  this,  using  the  protractor,  and  obtain 
your  answer  from  the  drawing. 

8.  If  the  sun  sets  N.  80°  W.  where  does    it    rise? 
Make  a  drawing  as  in  the  previous  question. 

7.     Telling  Time  by  the  Sun. 

In  olden  times,  before  clocks  were  made,  people 
used  to  tell  time  by  the  sun.  Even  now  there  are  many 
persons  who  can  judge  the  time  very  nearly,  by  the  posi- 
tion of  the  sun  in  the  sky.  Yet  it  is  impossible  to  learn 
the  time  from  the  sun,  with  exactness,  unless  we  make 
use  of  a  simple  piece  of  apparatus.  Just  a  stick  driven 
into  the  ground  is  all  that  is  necessary.  When  the 
shadow  points  north  it  is  noon.  See  Experiment  3. 
When  the  shadows  cast  at  sunrise  and  sunset  are  oppo- 
site each  other  the  time  of  each  is  six  o'clock.  If  the 
semi-circle  on  the  north  side  of  the  stick  is  divided  into 
twelve  equal  parts,  the  shadow  will  take  one  hour  to  pass 
over  each  part.  These  divisions  may  be  marked  with 
the  hours  between  six  in  the  morning  and  six  at  night. 
Over  how  many  degrees  does  the  shadow  move  in  one 
hour? 

Experiment  7. — The  Sundial. 
Apparatus:     Board,  protractor,  nail. 


TELLING  TIME  BY  THE  SUN  13 

a.  Draw  a  circle  on  a  board  using  the  protractor, 
and  divide  it  into  24  equal 
parts.  How  many  de- 
grees are  there  in  each 
part?  Drive  a  nail  into 
its  center  so  that  it  makes 
an  angle  of  90°  with  the 
board,  in  all  directions. 
You  can  do  this  by  hold- 
i  n  g  your  protractor 
against  the  nail  as  you 
drive  it.  Draw  a  line  from 
the  nail  lengthwise  of  the  board  and  place  the  board  so 
that  this  line  runs  north  and  south.  How  can  you  do  this? 
Mark  this  line  12,  where  it  crosses  the  circle  on  the 
north  side,  and  then  mark  the  other  divisions  properly 
Is  there  any  need  to  mark  all  of  the  divisions?  Why? 
What  time  does  the  shadow  tell  in  the  illustration? 


8.     Other  Ways  of  Telling  Time. 

The  sundial  is  a  good  way  of  telling  time  on  sunny 
days,  but  if  we  wrant  to  know  the  time  when  the  sun  is 
not  shining  we  must  use  other  methods.  Long  ago  the 
sand-glass,  or  hour-glass  was  invented  to  tell  the  length, 
of  an  hour.  This  was  made  by  connecting  two  bulbs  or 
globes  by  means  of  a  small  tube  and  having  one  glob^ 
filled  with  sand.  The  filled  globe  was  placed  on  top  and 
the  sand  slipped  slowly  through  the  small  hole  into  the 
lower  globe.  When  all  the  sand  had  left  the  upper  globe 
an  hour  had  passed.  Then  the  hour-glass  was  turned  up- 
side down  and  a  record  was  kept  of  the  number  of  hours. 
Why  was  the  name  hour-glass  given? 


14 


THE  SUN,  STARS,  AND  PLANETS 


An  ingenious  scheme  of  telling  time  was  by  means 
of  water.  Water  was  placed  in  a  tank  and  allowed  to 
flow  out  through  a  small  hole  into  a  little  tank  where 
there  was  a  float  made  of  wood.  As  the  water  rose  the 
float  rose  and  indicated  the  hours  by  marks  on  the  side 
of  the  little  tank.  Nowadays  clocks  are  used  in  which 
wheels  are  allowed  to  turn  slowly  by  means  of  a  pen- 
dulum. See  Section  64.  Next  year  we  shall  study  more 
about  clocks. 


Experiment  8. — The  Sand-glass. 
Apparatus:     Two  small  bottles,  two  stop- 
pers, a  piece  of  glass  tubing  y%"  diameter, 
small  triangular  file,  fine  sand. 

a.  Bore  a  hole  in  the  two  stoppers    for 
the  glass  tube  and    insert  the    tube  in    the 
stoppers  with  their  tops  together.  The  tube 
should  not  extend  beyond  the  stoppers.     Fill 
one  bottle  with  fine,   dry  sand,    insert    the 
stoppers  into  the  bottles  and  the  sand-glass 
is  finished. 

b.  How  long  does  it  take  for  the  sand  to 
run  through?       Keep  changing  the  amount 
of  sand  until  it  takes  exactly  one  minute,  or 
exactly    two  minutes    for  the  sand    to    run 
through.      Is  this  an  hour-glass?      A  sand- 
glass made  like  this  and  which  would  run 
for  three  and  a  half  or  four  minutes  would 
be  useful  for  timing  the  boiling  of  eggs. 


THE  HEIGHT  OF  THE  SUN  AT  NOON  15 

9.     The  Height  of  the  Sun  at  Noon. 

When  is  the  sun  highest  in  the  sky?  If  the  sun  is 
in  line  with  the  surface  of  the  earth  at  sunrise,  and  grad- 
ually becomes  higher  then  gradually  becomes  lower  un- 
til at  sunset  it  is  again  in  line  with  the  surface  of  the 
earth,  the  highest  point  must  have  been  reached  half- 
way between  sunrise  and  sunset.  What  time  is  this? 
What  can  you  say  about  the  length  of  shadows  at  sunrise 
and  at  noon?  At  sunset  and  at  noon?  When  is  the 
shortest  shadow?  Is  the  length  of  a  shadow  at  noon  al- 
ways the  same?  If  you  do  not  know,  how  are  you  going 
to  find  out?  The  varying  length  of  a  shadow  shows  the 
height  of  the  sun. 

Experiment  9. — The  Height  of  the  Sun  at  Noon  by 
Means  of  a  Shadow. 

a.  Measure  the  length  of  the  shadow  of  a  window- 
sill  where  the  sunlight  falls  upon  the  floor  at  noon. 

b.  One  week  later  measure    it    again.       Is    it    the 
same?     Continue  to  measure  the  shadow  once  a   week, 
keeping  a  record  of  the  lengths  similar    to    the    record 
used  in  Experiment  6.     Later  you  will  have  some  ques- 
tions about  this  experiment  to  answer.       See  Section  69. 


We  can  measure  the  height  of  trees  and  buildings 
and  mountains  in  feet  and  inches  but  we  cannot  measure 
the  height  of  the  sun  in  this  manner.  We  always  meas- 
ure the  height  of  the  sun  and  stars  by  the  number  of  de- 
grees which  we  have  to  look  upward  from  the  surface  of 
the  ocean  or  a  lake.  We  call  looking  along  the  surface  of 


16 


THE  SUN,  STARS,  AND  PLANETS 


Experiment  10. — The  Height  of  the  Sun  at  Noon 
Measured  in  Degrees. 

Apparatus:  Chalk  box,  protractor,  nail,  two  tacks, 
a  body  of  water  zero  degrees  high.  We  call  directly 
overhead  ninety  degrees  high. 

a.  Take  an  empty  chalk  box  and  with  the  open  side 
toward  you  tack  the  protractor  so  that  its  straight  side 
crosses  the  short  end  of  the  box  half-way  and  is  parallel 
with  the  long  side.  Drive  a  brad  at  the  center  point  of  the 
protractor.  With  your  rule  held  against  the  brad  and 
over  the  85  division,  mark  the  edge  of  the  box  with  pen- 
cil. Repeat  for  each  5°.  The  marks  on  the  edge  of  the 
chalk  box  are  not  the  same  distance  apart,  but  a  shadow 
of  the  nail  falls  on  each  mark  in  succession  for  each  5°. 
See  if  this  is  not  true.  The  apparatus  should  appear  like 
the  illustration. 


b.     Place  the  box  so  that  the  shadow  of  the  nail  at 
noon  falls. across  the  protractor  and  on  the  edge  of  the 


THE  HEIGHT  OF  THE  SUN  IN  DEGREES  17 

box.  What  is  the  number  of  degrees  that  the  sun  is  high 
at  noon?  Repeat  once  a  week  and  keep  a  record  as  in  the 
last  experiment.  Do  you  think  that  the  sun  is  ever  over- 
head? Can  you  find  out? 

Review  Questions,  4. 

1.  Xame  four  ways  of  telling  time. 

2.  When  did  the  sun  set  last  night?     Then   when 
did  the  sun  rise  yesterday? 

3.  If  the  hole  in  the  tube  of  the    hour-glass    were 
smaller  would  it  make  any  difference  in  the  time  which 
it  would  take  for  the  sand  to  run  through? 

4.  When  is  the  sun  the  highest  in  the  sky?     How 
can  you  tell  ? 

5.  What  are  the  two  ways  of  stating  how  high  the 
sun  is? 


Next  year  yon  will  learn  more  concerning  the  sun, 
stars,  and  planets.  Now  we  are  going  to  study  about 
what  we  receive  from  the  sun. 


Elem.  Sci    2 


THE  GUIDE 


LIGHT 

10.     The  Light  We  Receive  from  the  Sun. 

Just  after  sunrise  and  just  before  sunset  we  may  look 
at  the  sun  without  hurting  our  eyes.  The  sun  looks 
large  and  red.  The  reason  it  looks  large  is  because  we 
can  compare  its  size  with  the  size  of  other  objects,  and 
when  we  notice  that  it  appears  larger  than  a  distant  house 
or  tree  we  realize  that  it  is  very  large.  The  sun  appears 
red  because  the  light  in  coming  along  the  surface  of  the 
earth  has  passed  through  a  large  amount  of  dust  and  fine 
drops  of  water,  which  have  sifted  the  light  until  most  of 
its  strength  has  been  taken  out. 

As  the  sun  mounts  higher  and  higher  in  the  sky,  the 
light  passes  throueh  less  and  less  of  the  fine  particles, 
and  we  say  the  light  becomes  brighter.  On  hazy  days, 
or  when  there  is  smoke  in  the  air,  the  sun  looks  red  even 
at  noontime.  To  show  that  the  reason  why  the  sun  ap- 
pears red  is  because  the  light  is  sifted,  we  can  perform 
the  following  experiment. 

Experiment  11.— The  Appearance  of  the  Sun  through 
Smoked  Glass. 

Apparatus:     Glass,  candle. 

a.  Hold  a  piece  of  ordinary  window  glass    in    the 
flame  of  a  candle  or  the  flame  of  a  kerosene  lamp,  moving 
the  glass  around  in  order  to  distribute  the  smoke.       Tf 
the  glass  is  held  still  in  the  flame  it  will  break.       Smoke 
one  side  only.     The  material  on  the  glass  is  soot. 

b.  Hold  the  smoked  glass  between  the  sun  and  one 
of  your  eyes,  closing  the  other  one.     How  does  the  sun 
appear?     Move  the  glass  so  that  you  look  through  more 


20 


LIGHT 


or  less  soot.     How  does  the  color  of  the  sun  appear  to 


change? 


11.     The  Sunlight  Makes  Plants  Green. 

If  a  board  or  plank  is  laid  on  the  grass  for  several 
days,  so  that  the  sunlight  cannot  reach  it,  the  grass  will 
be  light  yellow,  and  even  white,  when  the  board  is  first 
removed.  In  a  few  days,  however,  the  grass  will  regain 
its  usual  green  color.  What  caused  the  change?  Pota- 
toes and  onions  which  sprout  in  the  dark  have  very  light 
green  or  light  yellow  stalks  and  leaves.  If  these  arc 
brought  into  the  sunlight  they  become  green.  Although 
plants  may  grow  in  the  dim  light  they  need  the  sunlight 
in  order  to  grow  well  and  to  bear  fruit. 

Experiment  12. — The  Effect  of  Sunlight  upon  Grow- 
ing Plants. 

a.     Cut  a  thin  slice  of  cork  from  a  stopper  and  trim 

it  into  some  shape,  such 
as  a  heart,  or  a  cross,  or 
a  clover  leaf,  and  pin  it 
upon  a  growing  leaf 
which  must  be  left  upon 
the  tree.  The  best  way 
to  fasten  the  piece  upon 
the  leaf  is  to  push  two 
pins  through  it,  through 
the  leaf,  and  into  another 
piece  of  cork,  which  is 
held  on  the  under  side  of 
the  leaf.  Do  not  touch  it 
for  one  week.  At  the  end 


EFFECT  OF  SUNLIGHT  ON  PLANTS  21 

of  a  week  remove  the  pieces  of  cork  and  report  how  the 
leaf  appears.  Let  the  leaf  remain  upon  the  tree  and  ex- 
amine it  at  the  end  of  another  week.  What  has  happened? 
b.  Try  other  designs  and  remove  the  leaves  from 
the  tree  when  the  cork  covers  are  removed.  See  who  can 
make  the  best  design. 

Review  Questions,  5. 

1.  Which  way  does  the  Great  Dipper  move   around 
the  North  Star,  clock-wise  or  the  other  way  around? 

2.  Look  at  the  Great  Dipper  as  early  as  you  can  see 
it  and  as  late  as  you  can  stay  up,  and  see  if  you  can  tell 
how  many  degrees  it  moves  in  one  hour. 

3.  If  the  sun  rises  exactly  in  the  east  and  sets  ex- 
actly in  the  west,  through  how  many    degrees    does    it 
move?     How  many  hours  does  it  take? 

4.  At  what  hour  does  the  sun  rise  when  it  rises  ex- 
actly in  the  east?     Through  how  many  degrees  does  the 
sun  move  in  one  hour? 

5.  Why  does  the  sun  appear  larger  at  sunrise  and 
sunset  than  it  does  at  noontime? 

6.  Why   does   the  sun   appear  red    at  sunrise    and 
sunset? 

7.  Is  it  ever  red  at  any  other  time?     Why? 

8.  What  makes  plants  green?     How  can  you  sho.v 
this?    ' 

9.  When  do  plants  grow  best0     \Vliv? 

10.  Did  you  obtain  your  answers  to  t'lese  qvicstinn  ; 
from  books?     What  is  the  best  way  of  ob fining  these 
answers? 


22  LIGHT 

12.     Other  Changes  of  Color  which  are    Caused  by    the 

Sunlight. 

If  we  are  out  in  the  sunlight  a  great  deal  our  skin 
becomes  brown  and  we  say  that  we  are  tanned.  This 
change  of  color  is  due  to  the  sun  and  it  takes  place  in 
order  to  protect  the  body  from  the  effects  of  too  much 
sunlight.  Some  persons  do  net  t'Mi  very  easily,  but  be- 
come red  and  often  blisters  are  caused  where  the  skin  has 
been  exposed  very  long  to  the  sunshine.  Even  persons 
who  do  tan  easily  are  sunburned  if  they  try  to  become 
tanned  in  a  few  days,  while  if  they  are  not  too  long  in 
the  sunlight  at  one  time,  the  skin  will  protect  itself  by 
putting  a  shield  between  the  sun  and  the  tender  inner 
skin.  Just  as  smoked  glass  shut  out  so  much  sunlight 
that  we  could  look  at  the  bright  'noonday  sun  without 
hurting  our  eyes,  so  the  tanned  skin  keeps  out  the  strong 
sunlight  and  we  can  expose  it  to  the  sun's  glare  without 
harm.  If  the  coloring  material  is  not  distributed  evenly 
throughout  the  skin  little  patches  come  which  are  called 
freckles. 

When  we  speak  of  the  sun  as  causing  plants  to  be 
green  and  the  skin  to  tan,  we  must  remember  that  the 
plants  and  the  skin  are  alive.  If  the  sun  shines  upon 
things  which  are  without  life  it  can  affect  the  color  which 
the  things  have,  causing  it  to  become  lighter,  and  in  some 
cases,  even  making  the  material  white  or  nearly  white. 
The  change  in  color  is  called  fading,  while  the  removal  of 
the  color  from  an  object  is  called  bleaching. 

Experiment  13: — Fading  and  Bleaching. 

a.  Obtain  several  pieces  of  differently-colored  cot- 
ton cloth  and  cut  each  piece  into  halves.  Keep  one  of 


FADING  AND  BLEACHING  23 

the  halves  of  each  piece  in  the  dark,  so  that  the  color  will 
hot  change.  Wet  the  other  halves  with  water  and  ex- 
pose them  to  the  bright  sunlight  until  there  is  a  change 
in  color.  The  pieces  should  be  kept  wet  and  it  may  take 
a  few  days  before  there  is  much  change.  Make  a  list  of 
the  colors  and  tell  how  soon  they  changed  and  what  each 
color  became. 

b.  Wet  and  expose  a  piece  of  unbleached  white  cot- 
ton cloth  to  the  bright  sunlight.  Compare  the  result 
with  another  piece  which  has  not  been  exposed. 

This  is  the  old-fashioned  way  of  bleaching  and  is  the 
best  method,  although  it  is  slow.  Bleaching  may  be  ac- 
complished much  more  quickly  by  the  use  of  chemicals, 
but  the  cloth  is  weakened  and  wears  out  more  quickly. 


The  sunlight  changes  the  color  of  certain  chemicals 
in  a  strange  way.  We  can  make  use  of  this  knowledge 
and  cause  the  sun  to  print  designs  for  us  on  paper.  The 
simplest  paper  for  this  purpose  is  called  blue-print  paper. 
It  may  be  purchased  cheaply  or  may  be  made  very  cheap- 
ly. See  Section  70. 

Experiment  14. — Blue  Prints  of  Leaves  and  other 
Articles. 

Apparatus :  Piece  of  window  glass,  leaves,  lace,  any 
thin  article,  blue-print  paper  at  least  4"x5". 

a.      Lay   a  piece  of  blue-print  paper  face  up  upon   a 


24 


LIGHT 


book.  Place  upon 
this  a  leaf,  a  piece  of 
lace,  or  any  thin  ar- 
ticle, and  cover  with 
the  piece  of  glass. 
Expose  to  the  bright 
sunlight  until  the 
color  of  the  paper  is 
a  bronze.  This  color 
must  be  learned  by 
experience.  When 
you  think  that  the 
color  is  right,  re- 
move the  paper  and 
wash  it  for  five  min- 
utes in  running  wa- 
ter, or  move  it  about 
in  a  basin  of  water.  The  exposed  part  of  the  paper  should 
be  a  dark  blue,  while  the  rest  should  be  a  pure  white.  If 
the  blue  color  is  not  dark,  it  means  that  you  did  not  leave 
the  paper  in  the  sunlight  long  enough.  If  the.  light 
part  is  not  white,  but  is  somewhat  blue,  it  is  because  you 
exposed  the  paper  too  long.  You  should  repeat  this  ex- 
periment at  home  until  you  can  obtain  clear  white  prints 
iiDon  a  dark  blue  surface. 

Blue-print  paper  will  also  be  used  in   Experiments 

68  and  75. 


Review  Questions,  6. 

1.     If  the  sun  should  rise  exactly  in  the  south-east, 
tell  exactly  where  it  would  set.     Why? 


SUNLIGHT  GOOD  FOR  PLANTS  AND  ANIMALS      25 

2.  If  the  sun  rises  at  six  o'clock  where  do  shadows 
point  at  that  time?       Can  you  devise  some  method    of 
telling  the  exact  east?     Can  you  do  this  by  means  of  the 
sunset? 

3.  Is  the  sun  ever  exactly  overhead?     If  it  should 
be  exactly  overhead  what  would  the  length  of  shadows 
be  then? 

4.  What  is  the  best  way  of  measuring  the  height 
of  the  sun  ? 

5.  How  could  you  make  a  yellow  figure  upon  a  red 
apple? 

6.  What  does  the  sun  do  to  your  skin?     Why  does 
this  happen? 

7.  What  does  the  sunlight  do  to  color? 

13.     The  Sunlight  Good  for  Plants  and  Animals. 

Although  plants  cannot  move  about  the  same  as 
animals,  they  do  turn  their  leaves  toward  the  sun  and 
even  grow  in  the  direction  of  the  sunlight.  Look  at  the 
plants  which  are  near  the  window  in  the  room,  and  notice 
how  they  lean  toward  the  sunlight.  This  shows  that  the 
sunlight  is  good  for  plants.  If  there  were  no  sunlight 
most  of  the  plants  would  soon  die. 

The  sunlight  is  also  good  for  animals  and  man.  If 
a  person  stays  indoors  too  much  he  will  become  sickly. 
We  should  be  out  in  the  sunlight  as  much  as  possible, 
and  our  buildings  and  houses  should  have  many  win- 
dows so  that  the  sunlight  can  enter  freely.  The  sun  has 
a  stimulating  effect  upon  the  body,  and  often  persons 
take  sunbaths  to  improve  their  general  health.  Taking 
a  sunbath  usually  means  sitting  in  the  sunshine,  but  in 
hospitals  they  are  given  by  having  the  patients  lie  on 
cots,  being  covered  only  by  a  sheet. 


26  LIGHT 

There  is  another  way  in  which  sunlight  helps  us  and 
that  is  by  killing  disease  germs.  Much  of  our  sickness 
is  caused  by  little  plants,  called  bacteria,  which  are  so 
small  that  they  cannot  be  seen.  These  plants  grow  best 
in  dark  and  damp  places  and  for  that  reason  we  should 
live  in  dry  and  sunny  houses.  If  the  sunlight  which 
comes  in  through  many  windows  is  too  much  for  our 
comfort  we  can  shut  it  out,  but  if  the  windows  are  too 
few  in  number  there  is  no  way  of  obtaining  enough  sun- 
light. Windows  are  as  cheap  as  the  wall  they  take  the 
place  of,  and  to  have  few  windows  is  no  economy. 

14.     Light  Travels  in  Straight  Lines. 

What  is  meant  by  a  straight  line?  When  we  say 
"As  straight  as  a  string,"  do  we  mean  a  tightly  pulled 
string  or  a  loose  string?  If  carpenters  wish  to  mark  a 
straight  line  on  a  building  they  rub  some  chalk  upon  a 
string,  stretch  it  tightly  where  they  desire  the  line,  and 
then  pulling  the  middle  out  a  little,  let  it  snap  back  upon 
the  wall.  Some  of  the  chalk  leaves  the  string  and  makes 
a  straight  line.  Why  is  the  line  straight?  Try  making 
straight  lines  with  a  chalk-line. 

Now  that  you  know  just  what  is  meant  by  the  word 
"straight"  you  can  see  that  light  travels  in  straight  lines 
If  there  is  a  candle  or  a  lamp  in  a  room,  can  you  go  any- 
where in  the  room  so  that  you  cannot  see  the  light?  How 
does  the  light  come  to  you  from  the  candle  or  lamp, 
straight  or  curved? 

Experiment  15. — The  Way   Light  Travels. 
Apparatus:     Slim    stick    three    or    four    feet    long, 
string,  two  pieces  of  cardboard,  candle. 


THE  PINHOLE  CAMERA  27 

a.     Make  a  bow  of  the  stick  by  means  of  the  string, 
having  the  string  come  over  the  ends  of  the  stick.    Sight 


along  the  tight  string  at  a  candle.     Does  the  light  come 
to  your  eye  in  a  straight  line? 

b.  Make  a  hole  with  your  pencil  point  through  the 
center  of  one  piece  of  cardboard,  and  hold  it  three  or  four 
inches  from  the  lighted  candle.  Hold  the  other  piece 
of  cardboard  near  the  first  piece,  on  the  side  away  from 
the  candle.  What  do  you  see?  A  darkened  room  is 
best  for  this  experiment.  If  you  do  not  see  anything 
distinctly  it  may  be  because  the  hole  is  either  too  large 
or  too  small.  What  you  see  is  an  image.  Explain  whv 
the  image  has  the  position  in  which  you  see  it?  If  light 
started  from  the  top  of  the  candle  and  passed  through 
the  hole,  in  a  straight  line,  would  it  strike  the  top  or  the 
bottom  of  the  second  piece  of  cardboard? 

Experiment  16.  —  How  to  Make  and  Use  a  Pin-hole 
Camera. 

Materials:  Chalk  box,  piece  of  ground  glass  to  fit 
as  cover  to  chalk  box,  tinfoil,  cardboard  box,  waxed  or 
greased  paper  to  cover  one  end  of  cardboard  box. 

a.  Cut  a  hole  in  the  center  of    the  bottom    of    the 
chalk  box  about  one-quarter  of  an  inch  across.       Cover 
this  hole  with  a  piece  of  tinfoil  and  make  a  pin-hole  in 
it.     Slide  the  ground  glass  into  the  chalk  box  as  a  cover. 
with  the  ground  side  out.     The  camera  is  finished. 

b.  Second  method.  —  Break  one  end  out  of  a  card- 
board box,  paste  the  cover  on,  and  cover  the  open  end 


28 


LIGHT 


with  waxed  paper,  or  paper  with  grease  on  it.  Make  a 
hole  with  a  pencil  point  in  the  end  of  the  box  which  is 
opposite  the  paper.  Both  cameras  may  be  used  in  the 
same  way,  but  the  first  one  will  give  better  images. 

c.  Turn  the  pin-hole  end  of  your  camera  toward 
the  objects  you  wish  to  see  in  the  camera.  Bright  ob- 
jects are  the  best  for  this  purpose.  Cover  the  head  and 
the  other  end  of  the  box  with  a  cloth,  or  a  jacket,  and  you 
will  see  an  image  in  all  its  natural  colors.  Where  is  the 
top  of  the  image?  Where  is  the  right  side  of  the  image? 
How  do  you  explain  this  result? 

Review  Questions,  7. 

1.  If  you  look  along  the  surface  of  a  body  of  water 
and  then  look  exactly  overhead,  through  how  many  de- 
grees have  you  tipped  your  head? 

2.  If  plants  die,  will  the  sun  make  the  leaves  green? 
What  besides  the  sunlight  is  necessary  in  order  that  the 
plants  be  green? 

3.  What  is  the  use  of  tan  upon  the  skin? 

What  is  the  harm  of  using  chemicals    to  bleach 


4. 
cloth? 

5. 
them  ? 


How  do  plants  show  that  sunlight  is  good  for 


THE  REFLECTION  OF  LIGHT  29 

6.  If  you  were  choosing  a  house  in  which  to  live, 
what  would  you  notice  especially? 

7.  Give  two  proofs  that  light    travels    in    straight 
lines. 

8.  Why  is  the  image  in  the  pin-hole  camera  upside 
down  ? 

15.     The  Reflection  of  Light. 

Light  travels  in  straight  lines  until  it  strikes  against 
something.  Then  it  is  turned  back,  and,  although  it  still 
travels  in  straight  lines,  the  direction  of  the  light  has 
been  changed.  This  turning,  or  bending,  of  light  is  called 
reflection.  When  the  object  which  causes  the  reflec- 
tion is  smooth  and  shiny  we  seem  to  see  the  light  in  the 
object.  If  you  look  at  the  reflection  of  any  object  in  a 
mirror,  it  seems  to  be  back  of  the  mirror.  This  is  called 
regular  reflection,  because  what  we  see  appears  just  like 
the  object.  The  appearance  of  an  object  in  a  mirror  is 
called  an  image.'  Can  you  imagine  why  it  is  called  an 
image? 

Experiment  17. — Reflection  from  Mirrors. 

Apparatus:  Mirror  at  least  2"x4",  block  of  wood 
2"x2"x4",  two  rubber  bands,  foot  rule,  pin. 

a.  Turn  the  mirror  toward  the  sun  but  tip  it  down- 
ward so  that  the  reflected  light  is  on  the  wall  about  as 
high  as  your  head.  Now  turn  the  mirror  about  45  de- 
grees to  the  right.  Through  how  many  degrees  does  the 
spot  of  light  move?  Repeat,  turning  the  mirror  to  the 
left.  What  result  do  you  obtain?  In  turning  the  mirror 
from  the  right  position  to  the  left  position  you  moved  it 


30 


LIGHT 


through  90  degrees.  Through  how  many  degrees  did 
the  spot  of  light  move?  Make  a  drawing  to  show  how 
the  light  came  from  the  sun  and  was  reflected  from  the 
mirror. 

b.     Fasten  the  mirror  to  the  block  of  wood  by  means 
of  the  rubber  bands,  and  place  it  on  a  board.       Stick  a 


pin  two  inches  in  front  of  the  mirror  and  place  the  rule 
so  that  its  end  touches  the  mirror  and  the  pin  comes  at 
the  two  inch  mark.  Look  in  the  mirror  and  tell  how  far 
back  of  the  mirror  the  image  of  the  pin  is.  Place  the  pin 
at  different  distances  and  repeat.  Having  made  several 
trials,  and  having  obtained  the  same  results  in  each  trial, 
you  can  now  draw  your  conclusions.  How  far  back  of 
the  mirror  is  the  image  compared  with  the  distance  the 
object  is  in  front  of  the  mirror? 


DIFFUSED  REFLECTION  OF  LIGHT  31 

If  the  object  upon  which  the  light  falls  is  rough  some 
of  the  light  is  reflected,  but,  since  the  rough  surface  is 
made  of  tiny  surfaces  which  face  in  all  directions,  the  light 
is  scattered  in  all  directions.  In  the  case  of  this  experi- 
ment we  cannot  see  the  sun  in  the  object  if  it  is  shining 
upon  it,  but  we  see  that  the  object  is  brighter.  We  call 
this  scattering  of  light,  diffused  reflection.  All  objects 
which  give  light  are  seen  by  the  light  which  they  pro- 
duce; all  other  objects  are  seen  by  the  light  which  they 
reflect.  Light  is  diffused  by  particles  of  dust  and  tiny 
drops  of  water  in  the  air  which  are  too  small  to  be  seen. 
The  light  which  we  receive  from  the  sky  and  from  clouds 
is  due  to  diffused  reflection.  Diffused  light  is  best  for 
the  eyes. 

Experiment  18. — Diffused  Reflection  of  Light. 
Apparatus:     Two  blackboard  erasers,  glass. 
Materials:     Little  milk,  sheet  of  white  paper. 

a.  Darken  the  room  except  for  one  window  through 
which  the  sunshine  is  coming.     Notice  the  particles    of 
dust  which  are  shining  by  reflected  light.     Stand  across 
the  room  and  look  for  the  particles  in  the  sunbeam.    Can 
you  see  them?     Why?      The  sky  is  bright  for  the  same 
reason  that  the  sunbeam  appears  to  be  bright.     If  there 
were  no    dust  in  the    air  you  could    not  see   a  sunbeam. 
Knock  two  blackboard  erasers  together  in  the    sunbeam 
and  tell  what  happens.     Look  at  your  companions'  faces 
as  you  do  this  and  see  if  they  become  brighter. 

b.  Put  a  glass  of  water  in  the  sunbeam  and  notice 
how  it  appears.     Now  add  a  drop  or  two  of  milk.     What 
color  does  the  water  become?     Could  you  see  a  glass  of 
water  across  the  room  better  if  there  were  a  few  drops 


32  LIGHT 

of  milk  in  it?  Why?  Add  some  more  milk  and  tell 
what  color  the  water  becomes.  When  only  a  little  light 
is  reflected  what  color  is  reflected?  Why  is  the  sky  bine? 
If  all  the  light  is  reflected  what  color  is  it? 

c.  Notice  the  amount  of  light  upon  the  ceiling.  Xow 
hold  a  sheet  of  white  paper  in  the  sunbeam  and  tell  what 
change  there  is  in  the  amount  of  light.  The  moon  shines 
by  light  reflected  from  the  sun,  so  moonlight  is  only  sun- 
light which  has  gone  to  the  moon  before  coming  to  us. 

Review  Questions,  8. 

1.  Face  the  north.     After  turning  135°  to  the  right, 
in  what  direction  are  you  facing?     If  you  had  turned  to 
the  left,  in  what  direction  would  you  be  facing? 

2.  If  the  sun  is  in  the  south  direction  every  day  in 
the  year,  at  noon,  how  can  the  sun  be  farther  south  in 
winter  than  in  summer? 

3.  If  the  sun  sets  at  quarter  before  seven  o'clock, 
at  vvhat  time  will  it  rise  next  day? 

4.  What  is  the  best  manner  of  finding  the  line  which 
is  half-way  between  the  shadows  in  Experiment  3? 

5.  What  is  the  cause  of  freckles?     Why  do  not  all 
persons  become  freckled? 

6.  If  you  looked  at    a    very    large    and    very  bright 
mirror  would  you  see  the  mirror?     Explain. 

7.  How  do  you  see  other  persons?       Do  they  give 
light? 

8.  If  you  are  five  feet  in  front  of  a  mirror  and   then 
move  three  feet  nearer,  how  much  nearer  are  you  to  your 
image? 

9.  Why    are    shades    used    over    lamps    and    other 

lights? 


SOURCES  OF  LIGHT  33 

10.  Why  is  the  sky  blue?  You  have  seen  the  sky 
when  it  is  nearly  white;  what  might  cause  a  clear  black 
sky? 

16.     Light  from  Sources  Other  Than  the  Sun. 

The  sun  is  by  far  the  best  source  of  light.  There 
is  no  light  so  powerful,  and  none  so  beneficial  to  plants 
and  animals.  Most  animals,  except  those  that  prowl  at 
night,  go  to  sleep  soon  after  sunset;  but  man  has  long 
been  accustomed  to  staying  awake  much  later.  The  need 
of  light  was  first  met  by  the  use  of  campfires.  If  a  per- 
son wished  to  leave  the  campfire  he  would  remove  a  burn- 
ing stick  or  fire-brand,  and  carry  it  with  him.  Thus  the 
torch  was  a  natural  outgrowth  from  the  campfire.  Later, 
man  learned  that  some  kinds  of  wood,  or  wood  which  had 
been  soaked  in  grease,  made  better  torches  than  a  fire- 
brand taken  from  the  campfire.  Still  later,  man  made 
lamps  in  which  wicks  burned  in  grease  or  oil.  The  flame 
was  uncovered  and  was  smoky  and  dim.  The  candle  was 
a  much  more  modern  invention  and,  as  you  know,  is  still 
used.  The  modern  oil  lamp,  having  the  flame  covered 
with  a  chimney  was  a  vast  improvement  over  the  ancient 
oil  or  grease  lamp.  The  burning  of  illuminating  gas  was 
the  next  advance  in  lighting  and  was  soon  followed  by  the 
electric  light. 

In  all  of  the  methods  of  producing  light,  except  by 
electricity,  we  obtain  more  heat  than  light  in  all  cases 
where  light  is  obtained  from  burning  a  material.  Even 
the  electric  light  produces  more  heat  than  light. 

Experiment  19. — Ordinary  Sources  of  Light. 

Apparatus:     Oil     lamp,     Bunsen     burner,     gasoline 

Elem.  Sci    3 


•  v 


34 


LIGHT 


lamp,  or  alcohol  lamp,  test  tubes,  test-tube  holder. 

Materials :  Pieces  of  wood,  candle,  iron  wire  No.  28, 
soft  coal. 

a.  Darken  the  room  as  much  as  possible.  Burn 
pieces  of  wood  (matches  will  do)  and  describe  the  light 
which  is  obtained.  Light  the  candle.  Is  the  light  steady? 
Why?  Light  the  kerosene  lamp  but  do  not  put  on  the 
chimney.  Describe  the  flame  and  light  obtained.  Would 
you  like  to  be  in  a  room  for  a  long  time  with  this  kind  of 
a  light?  Put  the  chimney  on  and  state  what  difference 
you  note. 

b.  If  there  is  gas  in  the  school,  light 
a  Bunsen  burner  and  describe  the 
light  when  the  dampers  at  the  bottom 
are  closed.  Open  the  dampers.  What 
is  the  difference  in  the  light?  Hold 
a  piece  of  No.  28  iron  wire,  coiled  into 
a  spiral,  in  the  flame.  Whe^  does  the 
light  come  from?  Light  the  alcohol 
lamp.  What  kind  of  light  does  burn- 
ing alcohol  give?  Could  you  read  by  it.  Hold  the  iron 


Cut  supplied  through  United   State   Department  of  Agriculture. 


COLD  LIGHT 


35 


spiral  in  the  flame.  Could  you  read  by  this 
light?  This  kind  of  light  is  called  secondary, 
because  it  is  caused  by  the  heat  of  the  flame, 
although  the  flame  gives  very  little  light.  First 
the  heat  comes  from  the  flame,  and  secondly 
the  light  comes  from  the  wire. 

c.  Put  a  few  pieces  of  wood,  or  soft  coal,  in 
a  test  tube  and  hold  it,  by  means  of  the  test- 
tube  holder,  in  the  alcohol  or  gas  flame.  Tell 
what  happens.  See  if  you  can  light  what  is 
coming  out  of  the  tube.  It  is  gas.  A  large 
amount  of  gas  is  made  by  heating  coal. 


While  the  heat  from  our  sources  of  light  is  very 
acceptable  during  cold  weather,  it  becomes  decidedly  un- 
pleasant on  the  hot  nights  when  we  must  use  lights. 
For  this  reason  scientists  are  trying  to  obtain  some 
source  of  light  which  will  produce  less  heat  than  any  we 
now.  use. 

The  whiter  the  light  the  less  heat  is  produced  com- 
pared with  the  intensity  of  the  light.  Thus  reddish  or 
yellowish  lights  produce  much  more  heat  than  light, 
while  white  light,  although  it  produces  a  large  amount 
of  heat,  yields  more  light  in  proportion.  Name  some 
yellow  lights  and  some  white  lights.  Nature  supplies  a 
yellowish  light  which  is  practically  cold.  Fireflies  and 
glowworms  are  examples  of  this  sort  of  light.  Try  to 
catch  some  glowworms  and  examine  them.  Decaying 
fishbones  sometimes  give  a  faint  light,  but,  like  the  light 
obtained  from  fireflies  and  glowworms,  is  of  no  practical 


36  LIGHT 

value.  This  kind  of  light  is  called  phosphorescence.  So 
far.  man  has  not  produced  any  really  cold  light  which  is 
sufficiently  strong  for  practical  purposes.  The  experi- 
ment shows  one  form  of  cold  light  which  is  used  to  a 
slight  extent  on  match-boxes,  clock  faces,  and  around 
door  bells  so  that  they  may  be  seen  in  the  dark. 

Experiment  20. — Cold   Light. 

Apparatus:     A  matchbox  with  the  word  "matches" 
made  of  luminous  paint. 

a.  Place  the  matchbox  so  that  the  direct    sunlight 
will  fall  upon  it  for  at  least  ten  minutes,  and  then  exam- 
ine it  in  a  dark  room.     It  may  be  necessary  to  remain 
in   the  dark  room   for  a  few   minutes  before    your  eyes 
will  become  accustomed  to  the  darkness.     What  do  yon 
see? 

b.  Keep  the  matchbox  in  a  perfectly  dark  place  for 
two  or  three  days  and  then  examine  it  without  removing 
it  from  the  dark.     Can  you  see  anything? 

c.  Place  the  matchbox  in  the  sunlight  for  ten  min- 
utes and  again  examine  in  a  dark  room.     What  do  you 
conclude  is  the  real  source  of    light  in  the  case  of  lumi- 
nous paints? 

Review  Questions,  9. 

1.  Which  side  of  trees  has  the  most  moss?     Why? 

2.  How  can  you  locate  the  south  by  means  of    a 
watch? 

3.  If  the  sun  rises  exactly  in  the  east,  what  is  the 
time  of  sunset? 

4.  Could  you  tell  time  by  the  Great  Dipper? 


REVIEW  QUESTIONS  37 

5.  What  are  some  of  the  advantages  of  sunlight? 

6.  What  are  the  two  kinds  of  reflection,  and  what 
is  the  chief  difference  between  them? 

7.  If  you  move  a  mirror  10°,  how  much  will    a    re- 
flected beam  of  sunlight  move? 

8.  What  are  some  of  the  sources  of  light? 

9.  Why  does  most  light  give  heat? 
10.     Give  examples  of  cold  light 


THE  QUIDS 


HEAT. 

17.     The  Heat  we  Receive  from  the  Sun. 

The  heat  which  we  receive  from  the  sun  is  necessary 
for  animal  life  and  for  plant  life.  As  you  know,  it  is 
useless  to  plant  seeds  in  very  cold  weather,  and  animals 
often  die  when  they  do  not  have  a  warm  place  in  which 
to  live.  (Later  we  shall  learn  more  about  the  effect  of 
heat  upon  plants.) 

Just  as  the  amount  of  light  which  we  receive  from 
the  sun  varies  with  the  different  seasons,  so  the  amouni 
of  heat  which  we  also  receive  from  the  sun  changes  from 
hour  to  hour  and  from  season  to  season.  When  is  the 
warmest  part  of  the  day?  When  is  the  coolest  part? 
Look  back  at  Section  10  and  try  to  explain  why  this  is 
so.  When  is  the  warmest  part  of  the  year?  When  is 
the  coldest  part?  Perhaps  you  may  obtain  a  suggestion 
from  Section  9.  The  next  experiment  will  show  why 
the  heat  from  the  sun  varies  as  it  does. 

Experiment  21. — *The  Varying  Heat  from  the  Sun. 

Apparatus:     Scissors,  protractor. 

Materials:     Cardboard  12"x8",  paper  staple. 

a.  Make  the  apparatus  as  shown  in  the  illustration. 
The  radius  of  the  quarter  circle  should  be  five  inches. 
The  divisions  numbered  1  to  44  should  be  one-fourth 
inch,  and  the  movable  strip  should  be  one  inch  wide.  One 
inch  of  the  end  of  the  strip  should  be  bent  up  and  a  quar- 
*  See  Section  62  before  performing  this  experiment. 


40 


HEAT 


ter  inch  hole  made  in  the  center.  The  line  of  divisions 
represents  the  surface  of  a  small  part  of  the  earth ;  the 
movable  piece  represents  a  sunbeam  one  inch  wide. 


When  this  "sunbeam"  is  perpendicu'ar  to  the  "surface 
of  the  earth"  it  covers  one  inch.  How  many  degrees 
are  needed  between  two  lines  to  make  them  perpendicular 
to  each  other?  If  the  "sunbeam"  is  at  any  other  angle 
it  covers  more  than  one  inch  of  the  "surface  of  the  earth." 
Now  if  you  had  just  enough  butter  to  cover  one  slice  of 
bread  but  had  to  cover  two  slices  with  it,  how  thick 
would  the  butter  be?  Suppose  that  you  were  so  un- 
fortunate as  to  be  obliged  to  cover  three  slices  with  the 
same  amount  of  butter,  how  thick  would  the  butter  be? 
In  a  manner  similar  to  this  the  sunshine  is  spread  "thick 
or  thin"  upon  the  surface  of  the  earth,  as  the  height  of 
the  sun  varies  with  the  time  of  day  and  with  the  changes 
of  season. 

b.  Place  your  apparatus  in  the  sunshine  early  in 
the  morning,  or  late  in  the  afternoon,  in  such  a  manner 
that  the  movable  arm  "sunbeam"  may  be  aimed  at  the 


AMOUNT   OF  HEAT   FROM   THE   SUN  41 

sun,  while  the  "surface  of  the  earth"  is  parallel  with  the 
real  surface  of  the  earth.  The  best  way  to  do  this  is  to 
place  the  arm  in  such  a  position  that  the  sun  shines 
through  the  hole  in  the  bent  end  and  falls  lengthwise 
along  the  middle  of  the  strip.  Read  the  angle  on  the 
protractor.  This  is  the  elevation  of  the  sun.  Count  the 
number  of  spaces  covered  by  the  ''sunbeam."  How 
strong  is  the  sunlight  compared  with  what  it  would  be 
if  it  were  perpendicular  to  the  "surface  of  the  earth?" 
Remember  your  buttered  bread! 

c.  Repeat   (b.)   at  noon.     What  is  the  elevation  of 
the  sun?     How  many  spaces  are  covered  by  the  "sun- 
beam"?    How  strong  is  the  sunlight  compared  with  what 
it  was  early  in  the  day? 

d.  Take  a  reading  once  a  week,  of  the  sun  at  noon 
and   the   number  of  spaces   covered  by   the  "sunbeam." 
Continue  this  experiment  the  rest  of  the  year.       Keep  a 
record   and   compare  it  with   the   record   which  you   are 
keeping  of  Experiment  10 


The  amount  of  heat  which  is  taken  up  by  different 
objects  is  very  different,  although  all  of  the  objects  may 
be  near  one  another  in  the  sunshine.  Shiny  objects  do 
not  become  very  warm  in  the  sunshine.  What  is  the 
effect  of  shiny  objects  upon  light?  They  do  the  same 
thing  to  heat  and  therefore  they  do  not  become  warm. 
White  objects  and  those  having  light  colors  also  are 
quite  cool  in  the  sunshine,  but  are  warmer  than  the 
shiny  objects  because  they  do  not  reflect  so  much  heat. 
Dark  colored  and  rough  objects  reflect  very  little  heat 


42  HEAT 

and  thus  become  very  warm.       What  color  of  clothing 
should  be  worn  in  hot  weather?     Why? 

Experiment  22. — The  Amount  of  Heat  Received  by 
Different  Colors. 

Apparatus:  Two  spice  cans  of  the  same  size,  kero- 
sene lamp,  pieces  of  paper,  white,  red,  yellow,  and  black. 

a.  Polish  one  spice  can  and  smoke  the  other  in  the 
flame  of  a  kerosene  lamp.  Fill  each  with  the  same  amount 
of  water  and  expose  both  in  the  bright  sunshine.         At 
the  end  of  twenty  minutes  dip  a  finger  into  each  and  tell 
what  the  difference  is  between  them.     See  Section  71. 

b.  While   waiting  for  the   water  to  become   warm 
expose  the  pieces  of  paper  to  the  bright  sunshine    and 
arrange  them  in  the  order  of  their  warmth,  putting    the 
hottest  one  first  and  the  coldest  one  last. 


We  have  seen  that  the  amount  of  heat  from  sunshine 
varies  with  the  altitude  of  the  sun,  because  when  the  sun 
is  low  a  given  amount  of  sunshine  is  spread  over  a  much 
greater  surface  than  when  the  sun  is  higher.  Do  you 
think  that  if  we  could  cause  more  sunshine  to  fall  upon 
a  certain  surface  it  would  become  warmer?  See  Experi- 
ment 17. 

There  is  another  means  by  which  light  and  heat 
may  be  gathered  together  so  that  what  falls  upon  a  large 
surface  is  caused  to  cover  only  a  very  small  surface. 
This  is  accomplished  by  the  use  of  a  circular  shaped 
piece  of  glass,  thicker  at  the  center  than  at  the  edges, 
called  a  lens,  or  "burning  glass." 


THE  "BURNING  GLASS"  43 

Experiment  23. —  "The 
Burning  Glass." 

Apparatus:  A  lens  at 
least  3"  in  diameter. 

Materials :  Bits  of 
paper,  cloth,  wood  and 
leather. 

a.  Hold  the  lens  flat 
to  the  light  as  it  comes 
from  the  sun  and  catch  the  light,  after  it  has  passed 
through  the  lens,  upon  a  piece  of  paper.  Move  the  lens 
toward  or  away  from  the  paper  until  the  spot  of  light  is  as 
small  as  possible.  Tell  what  happens.  Why  is  it  best  to 
have  the  spot  of  light  as  small  as  possible?  Repeat,  using 
cloth,  wood,  and  leather  in  the  place  of  paper.  Which 
do  you  think  would  become  hot  quicker,  black  or  white 
paper?  Try  it.  Notice  the  dark  ring  around  the  bright 
spot.  Where  has  the  light  gone? 

Review  Questions,  10. 

1.  What    is    the     difference    between     fading    and 
bleaching? 

2.  What  is  a  sunbath?     How  are  they  taken? 

3.  What  is  diffused  light?  How  can  it  be  produced? 

4.  Which  is  hotter,  red  light  or  white  light? 

5.  Give  some  examples  of  cold  light. 

6.  What  part  of  the  day  is  hottest?     Why? 

7.  What  material  becomes  the  hottest  in  the  sun- 
shine? 

8.  How  may  we  obtain  a  large  amount  of  the  sun's 
heat  in  a  very  small  space? 


44  HEAT 

9.  Write  to  pupils  in  schools  four  or  five  hundred 
miles  to  the  east  or  west  of  you,  and  ask  them  to  tell  you 
the  position  of  the  Great  Dipper  at  eight  o'clock.  . 

18.     Expansion  Due  to  Heat. 

Whenever  anything-  is  heated  it  becomes  larger. 
This  increase  in  size  is  called  expansion.  It  is  an  in- 
crease in  length,  breadth,  and  thickness.  In  liquids, 
such  as  water,  we  notice  the  increase  in  volume.  The 
increase  of  volume  is  also  evident  in  the  case  of  gases, 
of  which  air  is  an  example.  In  solids,  however,  it  is  the 
increase  in  length  only,  which  causes  us  to  be  watchful. 

The  next  time  you  are  near  a  railroad  track  look 
for  the  spaces  between  the  ends  of  the  rails.  Are  the 
spaces  large  or  small?  Is  the  day  hot  or  cold?  If  these 
spaces  were  not  left  when  the  rails  were  laid  in  cold 
weather,  they  would  expand  in  hot  weather  and  having 
no  space  in  which  to  expand,  would  bend  sidewise,  al- 
lowing the  car  wheels  to  leave  them.  If  you  were  lay- 
ing rails  on  a  very  hot  day  would  you  put  the  ends  close 
together,  or  would  you  leave  a  space  between  them? 

A  practical  use  of  expansion  due  to  heat  is  made  in 
putting  iron  tires  upon  wheels.  The  tires  are  quite  hot 
when  they  are  placed  around  the  wheel  and,  as  they  cool 
off  they  contract;  that  is,  become  smaller  and  thus  grip 
the  wheel  very  tightly.  See  Section  72. 

Experiment  24. — Heat  Causes  Expansion. 

Apparatus:  Lamp  chimney,  candle,  two  small 
blocks  of  wood,  iron  wire  No.  18,  rule,  4-ounce  bottle, 
cork  to  fit  bottle,  glass  tube  one  foot  long,  tumbler, 
alcohol  lamp  or  Bunsen  burner. 


HEAT  CAUSES  EXPANSION 


45 


a.  Arrange    appara- 
tus as  shown.  Light  the 
candle   and   immediate- 
ly mark  the  position  of 
the    end    of     the    wire. 
Watch  it  and  tell  what 
happens.     What  causes 
the  change?     Blow  out 
the  candle  and  explain 
what  happens. 

b.  Bore    a    hole     in 
the    cork     stopper     so 
that  the  glass  tube  will 
fit  it  snugly.     Push  the 
tube   into   the   hole    so 
that   the    end    is    even 
with   the   inner  side  of 


the  stopper,  and  insert  the  stopper  tightly  into 
the  bottle.  Place  the  other  end  in  a  tumbler  of 
water.  Warm  the  bottle  with  the  hands,  while 
watching  the  end  of  the  tube  which  is  under 
water.  What  happens?  Why?  Now  warm 
the  bottle  gently  with  a  flame?  What  occurs? 
Allow  the  bottle  to  cool.  What  do  you  see? 
Why?  As  the  air  cooled  it  contracted  thus 
occupying  less  room,  or  space.  The  surface  of 
the  water  in  the  tube  merely  fits  against  the  air. 


46 


HEAT 


c.  Fill  the  bottle  with  cold  water  and  in- 
sert the  stopper.  The  water  should  run  up 
the  tube  not  more  than  two  inches.  Mark  the 
surface  of  the  water  with  a  piece  of  string  tied 
tightly  around  the  tube.  Heat  the  bottle 
gently  and  tell  what  happens.  Explain.  Let 
the  water  cool  and  explain  what  happens. 


Some  materials  expand  more  than  others 
when  they  are  heated.  Thus  tin  expands 
twice  as  much  as  does  steel,  while  lead  and  zinc 
expand  still  more.  Steel  expands  the  least 
and  zinc  the  most.  This  difference  of  expan- 
sion leads  to  results  which  appear  strange  until 
we  think  about  what  is  occurring.  A  common  example  is 
the  loosening  of  preserve  jar  covers  when  the  jars  are 
turned  upside  down  and  the  covers  placed  in  hot  water. 
The  metal  cover  expands  more  than  the  glass  does  and 
becomes  loose. 

Experiment  25. — The  Result  of  Unequal  Expansion. 
Apparatus:     Apparatus  as  shown  in  cut,  consisting 


of  a  bar  of  brass  and  a  bar  of  iron  fastened  together, 
alcohol  or  gas  lamp,  bottle  to  hold  apparatus. 

Materials:     Ice,  salt. 

a.  Notice  that  the  bars  are  straight.  Heat  very 
hot  by  holding  the  bars  in  the  flame.  Which  way  do 
thev  bend,  with  the  brass  or  the  iron  outside?  Which 


UNEQUAL  EXPANSION 


expands  the  more,  brass  or  iron?     Let  the  bars  cool  and 
see  if  they  are  straight,  as  at  first. 

b.  Put  the  bars  in  salt  and  ice  and  let  them  become 
cool.  Which  way  do  they  bend?  A  metal  which,  when 
heated,  expands  faster  than  another  metal,  also  contracts 
faster  when  cooled.  The  unequal  expansion  of  metals 
is  made  use  of  for  practical  purposes.  The  illustration 
shows  a  strip  of  two  metals  which 
pre  joined  together  their  entire 
length,  and  then  bent  into  the 
shape  of  a  shepherd's  crook.  As 
the  metals  become  warmer,  due  to 
the  increased  warmth  of  a  room, 
the  metal  on  the  right  expands 
more  than  the  other  metal  and 
causes  them  both  to  bend  to  the 
left.  This  bending  brings  together 
the  double  metal  and  a  screw 
which  act  like  an  electric  push 
button.  Instead  of  ringing  a  bell, 
however,  the  electricity  changes 
the  dampers  of  the  furnace  so 
that  the  air  of  the  room  will  not 
be  so  warm.  When  the  room 
cools  off,  the  metals  bend  the 
other  way  and  cause  the  electric- 
ity to  open  the  dampers  again. 
The  machine  is  called  a  heat 
regulator  because  it  regulates 
the  amount  of  heat  which  a 
room  receives. 


Cut  supplied  by  the  Jewell  Heat  Regulator  Co. 


48  HEAT 

Review  Questions,  11. 

1.  What  are  the  advantages  of  a  sunny  house? 

2.  How  does  heat  come    to  us    from    the    sun,    in 
curves  or  in  straight  lines?     What  makes  you  think  so? 

3.  Wrhy  do  you  cover  your  head  when  you  look  at 
the  image  in  a  pin-hole  camera? 

4.  When  you  are  reading  at  night  should  you  have 
the  light  shining  directly  into  your  eyes?     How  should 
you  light  your  books? 

5.  Can  you  really  see  a  sunbeam ?What  do  you  see? 

6.  What  color  of  clothes  should  we  wear  in  sum- 
mer?      Why? 

7.  What  is  expansion  and  what  causes  it? 

8.  Do  all  things  expand  the  same  amount? 

19.     The  Thermometer  an  Application  of  Expansion. 

Is  it  warm  today?  How  do  you  judge?  If  you  have 
been  running  it  may  seem  warmer  to  you  than  to  some- 
one who  has  been  sitting  quietly.  The  best  way  to  learn 
about  the  warmth  is  by  means  of  a  thermometer.  This 
is  merely  a  tube  with  a  large  end  called  a  bulb,  and  is 
much  like  the  bottle  and  tube  which  was  used  in  Experi- 
ment 24,  c.  In  fact,  we  can  use  that  apparatus  in  the 
place  of  a  thermometer,  but  the  change  in  the  height  of 
the  water  would  be  too  little  to  measure  easily  for  ordi- 
nary changes  of  warmth.  We  saw,  however,  that  as  the 
water  became  warmer  it  expanded  and  ran  no  the  tube. 
When  anything  is  hot  we  say  that  it  has  a  high  temper- 
ature, and  when  it  is  cold  we  call  the  temperature  low. 
Thus  we  can  make  this  statement:  When  the  temper- 


THE  THERMOMETER  49 

ature  rose  the  water  rose  in  the  tube,  and  when  the 
temperature  went  down  the  water  also  went  down. 
Temperature  then,  is  the  condition  of  warmth,  high 
temperature  being  very  warm  and  low  temperature  very 
cold. 

The  usual  thermometer  is  a  very  thin  tube  closed 
at  one  end  and  with  a  bulb  at  the  other  end.  This  bulb 
may  contain  mercury,  sometimes  called 
quicksilver,  or  it  may  contain  colored 
alcohol.  It  is  the  mercury  or  alcohol  in 
the  bull)  which  expands  and  pushes  a  tiny 
thread  of  liquid  up  the  tube.  The  ther- 
mometer is  marked  either  on  the  glass  or 
en  the  back,  into  divisions  called  degrees, 
and  these  degrees  are  numbered  from  zero 
up  and  down.  There  are  two  kinds  of 
markings  on  thermometers.  The  ther- 
mometer which  is  used  ordinarily  is  called 
by  the  inventor's  name,  Fahrenheit,  and 
has  the  temperature  of  freezing  water 
marked  32  degrees,  and  the  temperature  of 
boiling  water  marked  212  degrees.  The 
illustration  shows  a  Fahrenheit  thermom- 
eter. The  other  thermometer  is  used  by 
scientists  everywhere,  and  in  many 
foreign  countries  by  everyone.  This  is 
called  the  Centigrade  thermometer  and  has 
the  freezing  temperature  of  water  marked 
0  degrees  and  the  boiling  temperature  of  water  marked 
100  degrees.  Of  course  the  temperature  of  freezing 
water  is  really  just  the  same  no  matter  what  it  is  called, 
just  as  you  are  the  same  person  whether  you  are  called  by 

Elem.  Sci.  4 


50  HEAT 

your  real  name  or  yonr  nickname ;  that  is,  32  degrees 
Fahrenheit  and  0  degrees  Centigrade  are  the  same  tem- 
perature. The  temperature  of  boiling  water  is  also  the 
same  although  it  is  called  212  degrees  Fahrenheit  and  100 
degrees  Centigrade.  If  you  do  not  state  whether  the  tem- 
perature is  according  to  the  Fahrenheit  thermometer  or 
the  Centigrade  thermometer,  it  is  understood  to  be  the 
Fahrenheit.  Degrees  are  marked  the  same  as  the  degrees 
of  a  circle,  that  is,  in  the  place  of  writing  60  degrees  Fah- 
renheit we  may  put  60° F. 

Experiment  26. — How  to  Read  a  Thermometer. 
Apparatus:     Cheap  thermometer. 

a.  Count  the  number  of  divisions  between  the  fig- 
ures 40  and  50.  How  manv  spaces  are  there?  What 
is  the  difference  between  40  and  50?  Then  how  many 
degrees  does  each  space  mark?  All  thermometers  are 
not  marked  the  same  and  you  should  find  out  every 
time  vou  use  a  thermometer  just  how  many  degrees  are 
covered  by  each  space. 

h.  Obtain  the  temperature  of  the  room.  To  do 
this  the  thermometer  should  come  to  rest,  that  is,  there 
should  be  no  difference  between  two  readings  taken  two 
or  three  minutes  apart.  The  temperature  of  a  room 
should  be  65  to  68  degrees  Fahrenheit  at  the  same  height 
as  the  heads  of  those  sitting.  If  the  temperature  out- 
doors is  more  than  68  degrees  the  temperature  indoor* 
may  be  uncomfortably  high,  but  we  should  try  to  keep 
the  temperature  at  68  degrees. 

c.  Take  the  outdoor  temperature  in  the  morning 
just  before  school  begins,  at  noon,  and  at  the  close  of 


TEMPERATURE— SENSATIONS 


51 


school.  Keep  a  record  of  the  temperature  and  you  can 
tell  the  hot  days  and  the  cold  days,  without  trusting  to 
your  memory.  A  record  is  to  be  trusted.  See  Section 
69. 

Another  practical  application  of  the  unequal  expan- 
sion of  metals  is  the  dial  thermometer.  You  have  all 
seen  thermometers  which  have  a  hand  moving  over  what 
appears  very  much  like  the  face  of  a  clock.  In  the  place 
of  the  hours,  however,  the  face  is  marked  into  divisions 
which  are  numbered  usually  from  zero  to  a  hundred  or 
more.  The  word  "Fah- 
renheit" generally  i  s 
printed  upon  the  face  of 
the  instrument.  The 
movement  of  the  hand 
is  caused  by  the  winding 
up,  or  the  unwinding,  of 
a  spiral,  due  to  the  un- 
equal expansion  of  the 
two  metals  of  which  it  is 
composed.  The  illustra- 
tion shows  the  spiral  but 
does  not  show  the  two 
metals.  Both  metals  are 
quite  thin  and  are  fast- 
ened together  their  entire  length  just  as  we  learned  the 
heat  regulator  was  made. 


We  should  not  depend  upon  our  feelings  in  regard 
to  temperature.     If  we  have  been  exercising  we  are  warm 

Cut  supplied  by  the  Standard  Thermometer  Co. 


52  HEAT 

and  may  endanger  our  health  by  remaining  in  a  room 
which  seems  comfortable,  when  really  it  is  too  cold. 
The  thermometer  is  the  only  true  guide  to  be  followed 
if  we  wish  to  know  the  real  temperature.  Of  course,  if 
we  are  exercising,  the  temperature  may  be  much  below 
68  degrees  and  do  us  no  harm.  The  temperature  of  68 
degrees  is  proper  for  persons  who  are  sitting  still,  or 
moving  about  only  a  little.  Is  your  room  at  the  right 
temperature? 

The  following  experiment  will  show  you  haw  little 
it  is  possible  to  trust  our  feelings  or  sensations, 

Experiment  27. — Hot  or  Cold? 

Apparatus:  Three  cups  or  other  similar  dishes, 
sauce  pan,  alcohol  or  gas  Tamp,  ring  standr  wire  gauze. 

Materials:     Ice. 

a.  Fill  one  cup  with  water  which  is  as  hot  as  yoif 
can  bear  putting  your  hand  into;  fill  the 
second  cup  with  water  at  the  temper- 
ature of  tfye  room  ;  the  third  cup  should 
be  filled  with  ice  cold  water.  Place  the 
fingers  of  one  hand  in  the  hot  water  and 
those  of  the  other  hand  in  the  very  cold 
water  and  let  them  remain  for  one  full 
minute.  Then  place  the  fingers  of  both 
hinds  in  the  cup  containing  the  water  ar 
the  temperature  of  the  room.  How  da 
the  fingers  feel?  Is  the  last  water  hot 
or  cold?  Can  you  trust  your  sensations?" 

Review  Questions,  12. 

1.  If  the  sun  rises  at  s«ven  o'clock,,  at  what  time 
will  it  set? 


HEAT  PRODUCES  LIGHT  53 

2.  On  which  side  of  a  street  is  it  better  to  live,  the 
north  side  or  the  south  side?       Before  answering  think 
where  the  sun  is  at  noon  and  the  direction  front  which 
the  sunshine  comes. 

3.  What  Is  one  thing  we  can  do  in  order  to  keep 
well  ? 

4.  How  may  we  obtain  light  from  a  flame    which 
gives  a  large  amount  of  heat  but  gives,  no  light  of  itself? 

5.  If  a  person  could  be  dressed  in  very  shiny  cloth- 
ing, just  like  a  mirror,  would  he  be  warm  or  cold  in  the 
sunshine?     Explain. 

6.  What  use  is  made  of  the  expansion  of  metals? 

7.  What  use  is  made  of  the  expansion  of  liquids? 

8.  How  do  you  read  a  thermometer? 

9.  If  the  temperature  in  the  morning  is  48° F.  and 
at  noon  it  is  65° F.,  what  has  been  the  change  in  temper- 
ature? 

10.  Why  should  we  not  depend  upon  owr  feelings 
concerning  the  temperature  of  a  room? 

20.    Heat  Produces  Light. 

In  Section  16  we  learned  that  heat  is  one  of  the 
sources  of  light  and  that  it  is  impossible,  as  far  as  we 
know  at  the  present  time,  to  produce  cold  light  which  is 
strong  enough  for  ordinary  use.  The  light  which  we 
obtain  from  heat,  however,  is  not  always  the  same,  for 
we  have  a  dull  red  light,  a  yellow  light  and  a  dazzling 
white  light.  What  causes  the  difference?  Did  you  ever 
see  a  blacksmith  working  at  his  anvil?  Sometimes  the 
iron  is  red-hot  when  he  removes  it  from  the  forge,  and 
sometimes  it  is  white-hot.  Now  you  know  the  difference, 

if  you  are  near  you  can  feel  the  difference. 


54  HEAT 

We  have  learned  that  water  boils  at  212°  Fahren- 
heit, and  we  have  always  thought  of  "boiling  hot"  as  being 
very  hot.  Of  course  we  have  known  that  the  fire  is  much 
hotter  but  we  have  never  thought  much  about  it.  Ice 
water  (32°F.)  is  changed  to  boiling  water  (212°F.)  by  an 
increase  of  180°,  yet  the  lowest  temperature  at  which 
there  is  a  dull  red  light  is  about  950°  Fahrenheit.  The 
temperature  of  bright  red  light  is  much  higher,  yellow 
light  is  caused  by  a  still  higher  temperature,  while  daz- 
zling white  light  is  caused  by  the  extremely  high  tem- 
perature of  2200° F.  The  electric  light  which  we  have  in 
our  houses  is  a  good  example  of  light  from  heat. 

21.     Heat  from  Friction. 

When  two  objects  are  rubbed  together  we  say  there 
is  friction  between  the  objects.  This  friction  makes  it 
hard  for  the  objects  to  move  past  each  other  and  it  re- 
quires more  strength  where  there  is  much  friction  than 
where  the  friction  is  less.  Oil  has  the  power  to  reduce 
the  friction  between  two  objects  and  for  that  reason  we 
oil  the  bearings  of  machinery,  also  the  curves  of  railroad 
tracks,  or  we  grease  the  places  where  we  want  one  part 
to  slip  easily  over  another  part.  Another  name  for 
oiling  is  lubricating. 

Try  rubbing  your  hands  together,  pressing  them 
firmly  against  each  other  and  moving  them  rapidly.  How 
do  they  feel?  Why  do  persons  rub  their  hands  together 
in  cold  weather?  Rub  a  coin  on  your  coat  sleeve  or  on 
the  carpet  and  tell  what  happens.  Feel  of  a  gimlet  after 
boring  a  hole,  and  explain  the  results.  Sometimes  the 
bearings  of  railroad  car  wheels  become  so  hot,  even  if 


FIRE-MAKING  55 

they  are  well  lubricated,  that  they  set  the  oil  on  fire,  and 
it  is  said  there  is  a  "hot  box." 

The  old  way  of  making  fire  depended  upon  friction. 
So  great  heat  can  be  produced  by  rapidly  rubbing  two 
sticks  together  that  they  may  be  caused  to  glow,  and  even 
burst  into  flame.  Indians  used  this  method  for  making 
fire  but  it  is  hard  to  do,  and  requires  skill  and  patience. 
There  is  an  easier  way  to  accomplish  the  same  result, 
which  we  will  now  try. 

Experiment  28. — Primitive  Fire-making. 

Materials:  Two  blocks  of  wood  2"x4"x6",  circular 
wooden  rod  7"long  and  pointed  at  both  ends,  a  bow  and 
string,  similar  to  the  one  used  in  Experiment  15,  lubricat- 
ing oil  or  grease. 

a.  Bore  a  hole  part  way  through  the  blocks  at  their 
center  points,  and  arrange  the  apparatus  as  shown  in  the 
illustration.  Lubricate  the  hole  in  the  top  block  but  put 
nothing  in  the  hole  in 
the  lower  block.  Why 
is  thh  done?  Bear  down 
hard  on  the  top  block 
and  move  the  bow  back- 
ward and  forward  very 
rapidly.  You  may  not 
be  able  to  make  the  lower  block  burn  but  you  should  be 
able  to  make  it  smoke.  Does  the  hole  in  the  upper  block 
become  equally  hot?  Why?  This  apparatus  is  called  a 
fire  drill ;  and  this  method  of  obtaining  fire  also  was  used 
in  olden  times. 

Another  method  of  making  fire  was  by  means  of  the 
flint  and  steel.  Flint  is  a  very  hard  stone  and  when  it  is 


56 


HEAT 


struck  against  iron  or  steel  it  removes  little  pieces,  and 
the  friction  is  so  great  that  they  become  almost  white 
hot.  These  tiny  particles  used  to  be  caught  upon  shred- 
ded linen,  called  tinder,  which  caught  fire  and  burned. 
As  soon  as  the  fire  was  obtained  the  tinder  was  covered 
up  and  kept  for  next  time. 

Flint  was  also  used  for  discharging  guns.  The 
hammer  of  the  gun  carried  a  piece  of  flint,  and  as  it  fell, 
it  touched  a  piece  of  steel  sending  a  shower  of  sparks 
down  into  the  powder.  These  guns  were  called  flint- 
locks. 

Experiment  29. — The  Flint  and  Steel  Gaslighter. 

Apparatus:     A  friction  gaslighter. 

Materials:     Alcohol,  piece  of  cloth. 

a.     Examine  the  lighter,  noticing  the  steel  file  and 


Cut  supplied  by  the  Safety  Gas  Lighter  Co. 


MATCHES  57 

the  material  which  rubs  against  it.  This  is  not  flint,  bu* 
the  action  of  the  lighter  is  very  much  like  the  old  flint 
and  steel. 

b.  Make  sparks  with  the  lighter.  To  do  so,  quickly 
rub  the  parts  together.  Feel  of  the  sparks.  Are  they 
hot?  Make  the  sparks  in  illuminating  gas.  Does  the 
gas  light?  If  there  is  no  gas  try  lighting  a  piece  of 
cloth  which  is  very  wet  with  alcohol.  Do  gas  and 
alcohol  have  to  be  very  warm  in  order  to  begin  to  burn? 


The  modern  way  of  obtaining  fire  is  by  means  of 
matches.  How  do  you  light  a  match?  What  causes  the 
match  to  light?  So  the  modern  way  is  much  like  the 
ancient  way,  after  all.  The  only  difference  is  that  the 
materials  on  the  head  of  the  match  begin  to  burn  at  a 
very  low  temperature,  just  as  gas  and  alcohol  were  set 
on  fire  by  sparks  which  were  not  noticeably  hot.  As 
soon  as  the  match  begins  to  burn  its  temperature  rises 
to  more  than  1000°F. 

Since  matches  are  so  easily  set  on  fire,  or  ignited,  as 
it  is  called,  they  should  be  kept  where  there  can  be  no 
friction.  It  is  not  safe  to  keep  them  in  the  cardboard  box 
in  which  they  are  sold,  for  sometimes  mice  gnaw  through 
these  boxes  and  ignite  the  matches  by  biting  them.  The 
best  way  in  which  to  keep  matches  is  in  a  tin  pail,  01  box, 
having  a  tightly  fitting  cover.  Not  only  is  that  the  safest 
way  but  the  covered  matches  will  also  be  kept  dry  and 
good. 


58  HEAT 

Review  Questions,  13. 

1.  What  is  the  color  of  the  sun  at  sunrise  and  sun- 
set?    Why  is  it  this  color? 

2.  Which  is  hotter,  red-hot  or  white-hot? 

3.  Why  does  the  sun  appear  red  when  you  look  at 
it  through  a  piece  of  smoked  glass? 

4.  In   what  direction   do  plants  grow    if  they    are 
placed  near  a  window?     Why? 

5.  What  is  a  straight  line?     How  can  you  make    a 
straight  line? 

6.  Why  do  we  receive  more  heat  from  the  sun    in 
summer  than  in  winter? 

7.  What  are  the  three  sources  of  heat  which  we  have 
studied? 

8.  What  would  be  the  result  if  you  did  not  lubricate 
the  hole  in  the  upper  block  in  Experiment  28? 

9.  What  are  the  sparks  when  flint    and    steel    are 
struck  together? 

10.  What  is  the  difference  between  the  modern  way 
of  making  fire  and  the  olden  way? 

22.     Heat  from  Combustion. 

By  far  the  greatest  amount  of  the  heat  which  we 
enjoy  comes  from  the  sun.  We  have  seen,  however,  that 
as  winter  draws  near  we  receive  less  and  less  heat  from 
the  sun,  so  that  it  becomes  necessary  for  us  to  obtain 
heat  from'  some  other  source.  Our  usual  source  of  heat 
is  from  the  burning  of  something.  Combustion  is 
another  name  for  burning. 

There  are  two  kinds  of  combustion,  complete    and 


HEAT  FROM  COMBUSTION  59 

incomplete.  By  complete  combustion  is  meant  that  all 
of  the  material  has  been  burned  and  none  wasted.  This 
can  be  accomplished  by  giving  the  fire  a  proper  amount 
of  air.  Did  you  ever  see  heavy,  black  smoke  coming  out 
a  chimney?  That  smoke  was  part  of  the  material  which 
should  have  been  burned  in  the  fire,  and  it  meant  a  loss 
to  the  one  who  was  running  the  fire.  The  smoke  showed 
that  there  was  incomplete  combustion.  If  the  com- 
bustion had  been  complete  there  would  have  been  no 
visible  smoke. 

There  are  other  reasons,  besides  economy,  why  fires 
should  not  be  allowed  to  send  off  vast  amounts  of  smoke. 
The  particles  of  smoke,  called  soot,  slowly  settle  and  spoil 
the  appearance  of  buildings,  soil  our  linen,  and  affect  our 
health.  It  is  very  bad  for  us  to  breathe  in  smoke  and 
soot.  In  many  cities  it  is  against  the  law  to  allow  chim- 
neys to  smoke  to  any  unnecessary  amount. 

Experiment  30. — Complete  and  Incomplete  Com- 
bustion. 

Apparatus:  Alcohol  lamp  filled  with  alcohol,  alcohol 
lamp  filled  with  turpentine,  Bunsen  burner. 

Materials:  Piece  of  broken  chinaware,  piece  of  iron 
wire  No.  28. 

a.  Light  the  alcohol  lamp.  Is  there 
any  smoke?  Is  the  flame  hot?  Hold  a 
piece  of  fine  iron  wire  in  the  flame  and 
notice  how  hot  it  becomes.  Hold  a  piece 
of  chinaware  in  the  flame.  Does  any- 
thing collect  upon  it? 

b.     Light  the  turpentine  lamp.     Is  there  any  smoke? 


60 


HEAT 


Is  the  flame  as  hot  as  the  flame  of  the  alcohol?      Why? 
Which  combustion  is  best? 

c.  Hold  a  piece    of  chinaware 
in    the    flame    of    the    turpentine 
lamp.       What    collects    upon    it? 
What  is  its  color? 

d.  Hold    the   piece    of    china- 
ware,   with    its    coating,    in    the 
flame  of  the  alcohol  lamp  for  sev- 
eral minutes.       What    does    this 
prove  about  the  wastefulness    of 
smoky  combustion? 

e.  Light    the    Bunsen    burner 
and   note    the   difference    in    the 
flame    when    the    air    vents    are 
closed  and   when  they  are  open. 
When  is  combustion  more  nearly 
perfect? 


Alt 


Ai? 


23.     Combustibles  and  Fuels. 

Anything  which  burns  is  a  combustible.  Fuels  are 
only  those  combustibles  which  we  ordinarily  burn  to 
produce  heat.  You  are  familiar  with  the  common  fuels 
which  are  coal,  coke,  wood,  charcoal,  oil  and  gas.  What 
do  you  notice  when  you  burn  them  ?  Do  they  all  burn 
with  a  flame? 

In  any  combustion  it  is  necessary  to  have  air.  In 
our  stoves  the  amount  of  air  is  regulated  by  dampers.  Do 
you  open  or  close  the  dampers  when  you  want  a  hot  fire? 
If  there  is  not  enough  air  the  fire  will  smoke,  and  finally 
go  out.  What  causes  incomplete  combustion? 


COMBUSTIBLES  61 

There  is  always  a  waste  in  the  burning  of  fuels,  even 
when  the  combustion  is  complete,  for  all  fuels,  except  oil 
and  gas,  contain  substances  which  do  not  burn.  These 
substances  produce  the  ashes  which  we  always  find  under 
our  fires.  These  ashes  often  contain  particles  of  fuel 
which  would  have  burned  if  the  fire  had  been  hotter,  so 
it  is  seen  that  there  are  two  losses  from  incomplete  com- 
bustion. What  are  they? 

All  combustibles,  except  some  oils  and  some  gases, 
come  directly  from  plants  or  animals.  The  following 
experiment  will  show  the  difference  between  the  two 
kinds  of  combustion. 


Experiment  31. — The  Combustion  of  Different  Ma- 
terials. 

Apparatus:     Alcohol  lamp  or  Bunsen  burner. 

Materials:  Wood,  charcoal,  coal,  coke,  paper,  straw, 
feathers,  piece  of  wool,  piece  of  silk,  piece  of  cotton,  piece 
of  linen,  whalebone,  piece  of  leather. 

a.  Hold  a  piece  of  each  material  in  the  flame  and 
note  how  it  burns.  Arrange  all  of  those  materials  which 
burn  easily  in  one  list  and  those  that  burn  slowly  in 
another  list.  Which  ones  come  from  animals  and  which 
from  plants?  Which  is  the  safest  clothing  to  wear  when 
near  flames,  cotton  or  woolen? 

Goods  may  be  prepared  so  that  they  will  not  burn 
readily.  This  is  called  fireproofing.  See  Section  73. 


62  HEAT 


24.     Flames. 

In  our  experiments  with  combustibles  we  found 
that,  while  some  of  them  burned  with  a  flame,  others  only 
glowed.  The  difference  is  caused  by  a  gas,  as  only  gases 
burn  with  a  flame.  But,  you  will  say,  you  saw  wood 
burn  with  a  flame,  and  wood  is  not  a  gas.  That  is  true, 
but  when  the  wood  is  heated  so  that  it  ignites,  part  of  it 
is  changed  into  a  gas  and  it  is  the  burning  of  this  gas 
which  causes  the  flame.  It  is  just  the  same  with  a  candle. 
The  wax,  when  it  is  heated,  changes  into  a  gas  and  the 
burning  gas  causes  the  flame.  Whenever  you  see  a 
flame  you  may  be  sure  that  a  gas  is  burning. 

There  are  two  kinds  of  flames,  those  which  give  a 
laro-e  amount  of  light  and  those  which  give  only  a  very 
little  light.  Those  flames  which  give  light  are  called 
luminous.  Can  you  name  some  luminous  flames?  Name 
one  flame  which  is  not  luminous.  How  can  you  obtain 
light  from  a  flame  which  is  not  luminous?  Luminous 
flames  show  that  the  combustion  is  not  complete,  the 
light  being  due  to  little  particles  which  are  not  hot 
enough  to  burn.  A  flame  which  can  hardly  be  seen  is 
the  result  of  very  nearly  complete  combustion,  and  these 
flames  are  much  hotter  than  the  luminous  flames. 

Experiment  32. — The  Cause  of  Flames. 

Apparatus:  Test  tube,  test-tube  holder,  alcohol 
lamp,  piece  of  glass  tubing  }/\"  thick,  4"  long. 

Materials:     Bits  of  wood,  candle. 

a.  Put  some  bits  of  wood  in  a  test  tube  and  heat 
them  in  the  flame  of  an  alcohol  lamp.  What  do  you  see 


THE  CAUSE  OF  FLAMES  63 

collecting  on  the  inside  of  the  test  tube? 
Continue  to  heat  the  wood  until  smoke 
comes  out  of  the  open  end.  Try  lighting 
this  with  a  match.  How  does  it  burn,  with 
a  flame  or  a  glow?  What  must  it  be? 
Where  did  it  come  from? 

b.  Continue  to  heat  the  bits  of  wood 
until  the  smoke  ceases  to  come  off,  then 
remove  from  the  flame.  After  the  tube 
has  cooled  a  little  pour  out  what  remains 
from  the  wood.  What  does  it  look  like? 
How  does  it  burn?  Why  does  it  burn 
this  way? 

c.  Light  a  candle,  let  it  burn  for  a  short 
.    .             ,,  time,  and  then  blow  it  out.     Have  a  burning 
\  '\        /7  match  all  ready  to  hold  over  the  candle.       It 

should  ignite.     What  burns? 

d.  Light  a  candle  and  hold  a  glass  tube  in 
the   flame  as  shown  in   the   illustration.       A 
gas  will  pass  up  the  tube  and  may  be  ignited 
at  the  top.     Where  does  the  gas  come  from? 

e.  If  there  is  gas,  try  the    experiment    as 
shown  in  the  illustration. 


Review  Questions,  14. 

1.  What  is  our  guide    from   which    we  may    learn 
direction  in  the  open  country?     How  can  you  find   the 
guide? 

2.  What  direction  is  45°  to  the  east  of  north?   What 
direction  is  S.  45° W?. 


64  HEAT 

3.  Can  you  see  a  light  in  the  dark.     Can  you  see   a 
person  in  the  dark?     Explain. 

4.  What  kind  of  light  is  best  for  the  eyes? 

5.  What  are  the  sources  of  heat? 

6.  When  you  see  smoke  coming  from  a  chimney  in 
large  quantities  what  do  you  know  about  the  fire  which 
causes  it? 

7.  What  is  the  difference  between  combustibles  and 
fuels? 

8.  Why  do  some  things  burn   with  a  flame    while 
others  only  glow  when  they  are  burning? 

9.  What  are    the    best    combustibles,    those    from 
plants  or  those  from  animals? 

10.  What  makes  a  flame  invisible? 

25.     First  Aid  to  the  Burned. 

If  the  clothing  is  on  fire  the  flames  may  be  slapped 
out,  unless  a  large  amount  of  the  clothing  is  burning.  Tn 
this  case  the  person  should  roll,  or  be  rolled,  upon  the 
floor.  This  crushes  out  the  flames.  Where  possible  the 
person  should  be  wrapped  in  any  heavy  material,  such  as 
a  mat  or  a  rug,  or  even  a  coat.  The  wrapping  should  be 
very  tight.  The  person  should  not  be  allowed  to  stand, 
as  the  flames  will  rush  upward,  setting  more  of  the  cloth- 
ing on  fire,  and  perhaps  causing  the  person  to  breathe 
the  flame,  which  is  very  dangerous.  Under  no  circum- 
stance should  the  person  be  allowed  to  run  about.  If 
persons  would  act  quickly,  harmful  and  even  many  a 
dangerous  burning  accident  could  be  avoided.  Be  quick  ! 

Experiment  33. — Drill  for  Extinguishing  Burning 
Clothing. 


THE  TREATMENT  OF  BURNS  65 

Apparatus:     Children. 

Materials:     Rug  or  coat. 

a.  Let  one  child  be  supposed  to  have  burning  cloth- 
ing and  let  two  or  three  other  children  slap  out  the  imag- 
inary flames,  and  wrap  the  burning  child  in  a  rug  or 
coat,  and  roll  him  upon  the  floor. 

The  pupils  who  do  this  should  be  those  who  are 'best 
fitted  to  illustrate  the  method  for  the  class.  As  other 
pupils  improve  they  should  be  allowed  to  show  the  class 
this  drill,  perhaps  at  the  end  of  each  month. 


The  treatment  of  burns  which  are  not  severe  is  very 
simple.  Just  moisten  the  burnt  part  with  warm  or  cold 
water  and  put  on  all  the  baking  soda  which  will  stick.  If 
the  burn  is  quite  bad,  but  has  not  blistered,  the  baking 
soda  may  be  bandaged  on  the  burn  with  clean  cloth  which 
has  been  torn  into  strips  three-fourth  of  an  inch  wide. 

If  the  burns  are  serious  the  water  blisters  should  be 
pricked  with  a  needle,  which  has  been  heated  ret-hot  and 
used  as  soon  as  cool,  to  allow  the  water  to  run  out,  and 
then  apply  a  mixture  of  equal  parts  limewater  and  olive 
oil.  Cover  the  burn  with  absorbent  cotton  which  has 
been  soaked  in  the  same  mixture,  and  bandage  snugly, 
but  not  tightly.  If  the  burns  are  very  serious  it  is  best 
to  call  a  physician. 

Limewater  may  be  prepared  by  putting  one  ounce  of 
fresh  unslaked  lime  into  a  pint  of  cold  water,  shaking 
until  the  lime  breaks  up,  and  allowing  to  settle.  The 
clear  liquid  should  be  poured  off  the  top  and  kept  in  well- 
stoppered  bottles.  A  bottle  containing  equal  parts  of 

Elem.  Sci.  5 


66  HEAT 

lime-water  and  olive  oil  should  be  kept  in  every  kitchen. 
If  limewater  is  not  at  hand,  use  baking  soda  and  olive  oil. 

Any  of  the  following  materials  may  be  used  for 
burns:  baking  soda,  olive  oil,  limewater,  white  lead  and 
linseed  oil,  powdered  chalk,  cornstarch,  laundry  starch, 
flour  of  any  kind,  mucilage  or  dissolved  gelatine  covered 
with  any  of  the  powders  mentioned  above.  Since  quick- 
ness means  much  to  the  patient,  ease  in  obtaining  the 
remedy  should  have  first  consideration. 

There  is  another  danger  which  is  connected  with 
burns  because  the  skin  is  usually  destroyed.  This  gives 
the  bacteria  a  chance  to  enter  and  produce  trouble  for  us. 
To  overcome  these  little  plants  we  must  bathe  the 
affected  parts  with  some  material  which  is  an  antiseptic, 
that  is,  something  which  is  against  the  poisoning.  We 
should  do  this  whenever  we  break  our  skin  by  any  means. 
There  are  many  antiseptic  washes  to  be  obtained  in  drug 
stores  and  the  proper  kind  can  always  be  obtained. 

Heat  is  harmful  to  bacteria  if  the  temperature  is 
212°  F.  Where  articles  are  known  to  contain  bacteria 
they  may  be  killed  by  keeping  them  at  the  boiling  point 
of  water  for  twenty  minutes,  or  a  shorter  time  at  a  higher 
temnerature. 


26.     Conduction  of  Heat. 

When  we  use  a  stove-poker  for  a  few  minutes,  the 
part  which  we  are  holding  becomes  uncomfortably  hot. 
We  call  this  travelling  of  heat  along  an  object,  conduction. 
Tf  the  heat  reaches  the  cold  end  quickly,  we  say  that  the 
material  is  a  good  conductor. 

If  we  put  a  wooden  handle  on  our  poker,  we    may 


CONDUCTION  OF  HEAT  67 

poke  as  long  as  we  wish  and  our  hands  will  not  be  burned. 
That  is  because  wood  is  a  poor  conductor.  Most  metals 
are  good  conductors  of  heat,  although  some  metals  do 
not  conduct  heat  as  well  as  others.  Water  is  a  poor  con- 
ductor of  heat. 

Experiment  34. — Good  and  Poor  Conductors  of  Heat. 

Apparatus:     Alcohol  or  gas  lamp,  pieces  of  copper 
and  iron  wires  No.  12,  6"long,  test  tube. 

a.  Hold  the  end  of  the  copper  wire  in  one  hand  and 
the  end  of  the  iron  wire  in  the  other  hand,  and  put  the 
free  ends  into  the  flame  of  a  burner.       Which  one  be- 
came warm  first?     Which  is  the  better  conductor?    Hold 
the  poor  conductor  in  the  flame  and  notice  that  it  takes 
a  long  time  to  become  hot  at  the  hand. 

b.  Fill  the  test  tube  nearly  full  of  water  and  place 
as  shown  in  the  flame  of  a  burner,  so  that  the  top  of  the 
water  is  heated.     Do  not  let  the  flame  touch  the  glass 
where  there  is  no  water,  as 

it  will  break.  When  the 
water  boils  at  the  top  how 
it  the  bottom?  Is  water  a 
§food  or  a  poor  conductor  oi 
heat?  If  vou  wanted  tn 
heat  water  where  would  you 
heat  it,  at  the  bottom  or 
top?  How  does  the  ocean 
become  heated,  at  the  top  or 
the  bottom? 


68  HEAT 

If  a  substance  is  a  good  conductor  of  heat  and  it  is 
colder  than  our  bodies,  it  will  take  heat  away  from  us  if 
we  touch  it,  and  we  will  say  that  the  body  is  cold.  Yet 
there  may  be  another  substance  which  is  just  as  cold  as 
the  first  one,  but  is  a  poor  conductor  of  heat,  and  this  one 
will  not  conduct  the  heat  away  from  us,  and  we  may  say 
that  it  is  warm.  Thus  we  find  that  standing  with  bare 
feet  upon  a  rug  is  pleasanter  than  standing  upon  the  bare 
floor,  or  upon  an  oilcloth.  The  rug  is  not  a  conductor  of 
heat.  It  is  called  a  non-conductor.  Therefore  our  feet 
remain  warm.  The  oilcloth,  or  the  bare  floor,  is  a  much 
better  conductor  of  heat  and  takes  it  away  from  our  feet 
and  they  feel  cold.  Linen,  cotton,  and  silk  feel  cold 
because  they  are  good  conductors,  while  woolen  goods 
and  furs  feel  warm  because  they  are  poor  conductors  of 
heat.  Poor  conductors  make  the  warmest  clothing. 

If  the  substance  is  warmer  than  we  are,  and  is  a 
jrood  conductor,  it  feels  warm  because  it  readily  gives 
its  heat  to  us.  A  non-conductor  does  not  seern  as  warm, 
although  it  may  be.  warmer,  because  it  does  not  conduct 
the  heat  to  us.  Here  again  we  must  not  trust  our  sensa- 
tions but  must  depend  upon  a  thermometer,  if  we  wish 
to  learn  the  real  temperature  of  the  substance. 

It  is  not  a  good  plan  to  stand  upon,  or  sit  upon, 
materials  which  are  good  conductors,  when  they  are 
colder  than  we  are,  for  they  take  our  heat  away  and 
make  us  cold.  Stones  are  good  conductors  and  many  a 
chill  has  been  caused  by  sitting  upon  stone  walls. 

If  heat  is  not  desired  it  may  be  kept  out  by  the  use 
of  non  -  conductors.  For  this  reason  milk  cans  are 
wrapped  in  jackets  to  keep  out  the  heat  of  the  sun  on  hot 
days. 


REVIEW  QUESTIONS  69 

Review  Questions,  15, 

1.  What  makes  the  sun  appear  red  and  large  at  sun- 
rise and  sunset?       Does  the  sun  really  change  its  color 
and  size? 

2.  What  causes  the  sky  to  be  light  blue  on  some 
days  arid  dark  blue  on  other  days? 

3.  When  you  pour  hot  water  into  a  glass  dish  the 
inside  expands  before  the  heat  reaches  the  outside.  What 
happens?     Is  glass  a  good  conductor  of  heat?       Do  you 
think  thin  glass  would  break? 

4.  What  is  friction?     How  can  you  make  friction 
much  less  than  it  would  be  if  you  did  nothing? 

5.  Why  do  we  build  a  fire  by  first  putting  in  paper, 
then  little  pieces  of  wood,    and  finally    large    pieces    of 
wood,  or  perhaps  coal? 

6.  What  must  be  done  if  the  clothing  is  on  fire? 

7.  What  is  the  most  common  remedy  for  burns? 

8.  Why  do  linen  sheets  feel  cold  when  we  first  get 
into  bed? 

9.  How  does  the  teakettle  become  warm  when    on 
top  of  the  stove? 

10.  Why  do  firemen  wear  woolen  shirts?     Give  two 
reasons. 


THE  GUIDE 


AIR, 

27.     Air  a  Necessity  of  Life, 

There  can  be  no  life  of  any  sort  without  air.  Ani- 
mals breathe  it  and  plants  need  it,  in  order  to  live.  There 
is  air  even  in  water  and  fishes  could  not  live  without 
this  air.  We  live  in  an  ocean  of  air  which  surrounds  the 
whole  earth  and  this  ocean  is  called  the  atmosphere.  The 
meaning  of  the  word  "atmosphere"  is  breath-sphere.  Do 
you  think  that  the  atmosphere  is  well  named? 

Experiment  35. — Holding  the  Breath  and  Deep 
Breathing-. 

a.  See    how    many    seconds    you    can    hold    your 
breath.     You  should  be  able  to  hold  it  one  minute,  with 
practice. 

b.  Stand  erect  with  the  chest  up,  without  having 
any  of  your  muscles  hard  and  take  just  as  long  a  breath 
as  you  can,  breathing   through    the    nose.       When    you 
think  that  you  cannot  draw  in,  or  inhale,  any  more  air, 
contract  all  the  muscles  of  the  body,  and  hold  the  breath 
for  a  few  seconds.     Slowly  let  the  air  come  out.     Letting 
the  air  out  is  called  exhaling.     Repeat  several  times  and 
then  see  how  long  you  can  hold  your  breath.       Always 
take  this  exercise  before  holding  your  breath.      Why  can 
you  hold  it  longer  than  you  did  at  first? 

Experiment  36. — *The  Effect  of  Depriving  a  Plant 
of  Air. 

*  Adapted  from  Farmers'  Bulletin  409,  U.  S.  Dept.  of  Agriculture. 


72 


AIR 


Apparatus:  Two  glasses  or  bottles,  burner,  stand, 
dish  for  heating. 

Materials:     Geranium  cuttings,  olive  oil,  cardboard. 

a.  Heat  the  water  slowly.     What  comes  out  of  the 
water  long  before  it  boils?       Boil  the  water  for  two    or 
three  minutes  and  allow  it  to  cool. 

b.  Fill  one  of  the  glasses  two-thirds  full  of  water 
which  has  not  been  boiled,  and  fill  the  other  glass    two- 
third    full    of   the   boiled    water, 
after  it  has  become  cold.     Pre- 
pare  two   cardboard   covers,    as 
shown    in    the    illustration,     and 
put  a  geranium  cutting  in  each. 
Po*ir  olive  oil  on  the  surface  of 
the  boiled  water  to  a  depth  of  a 
quarter  of  an  inch,  being  careful 
not  to  get  the  oil  upon  the  cut 

end  of  the  geranium  slip.  Watch  the  cuttings  for  a  week 
or  ten  days  and  note  the  difference  between  the  growth 
of  roots  upon  the  two  cuttings.  Do  plants  need  air  in 
order  that  their  roots  may  grow? 

28.     Air  in  the  Soil  and  in  Water. 

If  we  take  a  handful  of  soil  and  examine  it  we  will 
notice  that  it  is  made  up  of  many  fine  particles  of  irregu- 
lar shape  and  size,  which  do  not  fit  tightly  together.  Thus 
there  are  left  a  large  number  of  tiny  holes  between  the 
little  particles,  which  all  added  make  a  large  space.  These 
spaces  are  all  filled  with  air. 

When  the  sun  is  shining  upon  the  soil  it  becomes 
warm  and  the  air  in  it  expands,  and  some  of  it  comes  out 
of  the  soil.  As  the  ground  cools  off  at  night,  the  air  within 


Cut  supplied  through  United  States  Department  of  Agriculture. 


AIR  IN  SOIL  AND  WATER 


73 


the  soil  contracts  again  and  more  air  enters  to  take  the 
place  left  by  the  contraction.  Since  plant  roots  need  air, 
can  you  see  the  advantage  of  cool  nights  during  the  sum- 
mer? 

Water  also  contains  air,  as  was  learned  from  the  last 
experiment.  In  the  next  experiment  we  will  see  just 
how  much  air  is  held  in  water  when  it  is  cold. 

Experiment  37. — To  Show  the  Presence  of  Air  in 
Soil  and  Water. 

Apparatus:  Tin  can,  glass,  two  test  tubes,  one-hole 
stopper,  glass  tube  two  feet  long,  burner. 

Materials:     Soil,  water. 

a.  Fill  the  tin  can  nearly  full  of  dry  soil,    loosely 
packed,  and  quickly  pour  a  glassful   of  water  upon    it. 
What  do  you  notice?       What  can  you  say    about    the 
presence  of  air  in  soil? 

b.  Throw  away  the  wet  soil  and    fill    again    with 
loosely  packed,  dry  soil.     Fill  the  glass  even 

full  of  water  and  pour  it  slowly  upon  the  soil, 
not  allowing  the  top  of  the  soil  to  be  covered 
with  water  at  any  time.  Continue  to  add 
water  until  the  soil  will  take  no  more  and  the 
water  surface  comes  up  to  the  surface  of  the 
soil.  How  much  water  have  you  added? 
How  much  air  was  there  in  the  soil? 

c.  Arrange  the  apparatus  as  shown  in  the 
illustration.  To  bend  glass  tubing  it  should 
be  held  in  the  flame  of  an  ordinary  gas 
burner,  or  an  alcohol  lamp,  or  in  the  flame 
produced  by  an  attachment  for  the  Bunsen 
burner,  as  shown  in  the  illustration,  called  a 


74 


AIR 


wing  top  burner.  At  least 
two  inches  of  the  tube  should 
be  heated,  and  it  should  be 
turned  slowly  so  that  all  sides 
may  receive  the  same  amount 
of  heat.  When  the  glass  has 
become  soft,  it  should  be  re- 
moved from  the  flame  and  quickly  bent  at  right  angles 
and  held  in  this  position  until  it  has  hardened.  If  the 
bend  is  not  well  rounded  it  shows  that  the  glass  was  not 
evenly  heated.  The  second  bend  is  to  be  made  in  the 
same  way. 

Fill  the  test  tube  full  of  cold  water  and  after  properly 
arranging  the  apparatus,  gently  heat  it.  The  outlet  tube 
should  dip  into  a  little  water.  As  the  water  is  heated  it 
expands  and  passes  over  into  the  other  test  tube.  Do 
you  see  any  air  collecting  in  the  heated  tube?  Where 
does  it  come  from?  If  the  water  is  heated  too  much  it 
will  begin  to  boil  and  may  force  most  of  itself  over  into 
the  other  tube.  It  is  not  necessary  to  heat  it  until  it 
boils.  Allow  the  water  to  cool  and  notice  what  part  of 
the  tube  is  occupied  by  air.  This  is  the  air  which  fishes 
use,  and  they  could  not  live  in  water  which  had  been 
boiled  and  then  cooled. 

Review  Questions,  16. 

1.  Which  kind  of  soil  will  become  the  warmer  in 
the  sunshine,  dark   colored  or  light  colored?      Which  is 
best  for  early  planting? 

2.  When  is  the  sunshine  warmer,  when    the    sun 
appears  red  or  when  it  appears  white? 

3.  How  many  degrees  away  from  the  direction    of 


THE  COMPOSITION  OF  THE  ATMOSPHERE        75 

a  shadow  is  the  direction  of  the  light?       How  do  you 
define  these  two  directions? 

4.  How  can  you    tell  the    time  of  sunrise    if    you 
know  the  time  of  sunset? 

5.  What  is  the  proper  temperature  for  the  school- 
room and  the  home? 

6.  Why  does  the  ground  become  warm  faster  than 
a  pond? 

7.  Which  will  burn  us  the  more,  a  piece  of  wood 
or   a  piece    of  copper,    if  both    are  at    the  same    temper- 
ature?    Explain. 

8.  Where  do  we  live  in  our  ocean  of  air,  at  the  bot- 
tom or  the  top?     Could  we  live  anywhere  else  than  where 
we  do? 

9.  Would  it  do  any  harm  to  water  plants  so  much 
that  the  ground  would  be  covered  with  water? 

10.  What  collects  on  the  inside  of  a  glass    of   cold 
water  if  left  in  a  warm  room? 

29.     The  Composition  of  the  Atmosphere. 

Some  mornings  when  you  come  to  school  it  is  fogg> 
and  you  think  how  damp  the  air  is.  Even  if  it  is  not 
foggy  you  have  often  noticed  that  the  air  is  damp  and 
you  have  heard  persons  say,  "Clothes  will  not  dry  today." 
On  other  days,  however,  it  has  been  brisk  and  bracing 
and  the  air  has  been  called  dry.  Though  the  air  has 
seemed  dry  it  still  contained  water  in  an  invisible  form. 
It  is  from  the  invisible  form  of  water  that  dew,  fog,  and 
clouds  are  formed. 

The  amount  of  water  in  the  air  varies  from  day  to 
day  and  even  from  hour  to  hour.  The  air  near  large 
bodies  of  water  usually  contains  more  moisture  than 


76 


AIR 


does  the  air  in  other  places.  Why?  If  you  leave  a 
glass  of  cold  water  in  a  warm  room,  what  collects  on  the 
outside?  There  is  another  part  of  the  atmosphere  called 
carbon  dioxide,  which  also  varies  according  to  the  local- 
ity. In  the  open  country  there  is  very  little  of  this  gas, 
but  in  cities,  and  in  rooms  where  there  are  a  large  num- 
ber of  persons,  it  may  increase  so  as  to  harm  us,  for  it 
is  not  a  good  gas  to  breathe. 

Although  the  amount  of  water  and  carbon  dioxide 
in  the  atmosphere  varies  greatly,  the  largest  portion  of 
the  air  is  composed  of  two  gases  which  do  not  vary 
About  one-fifth  of  the  air  is  oxygen,  and  about  four- 
fifths  is  nitrogen.  These  gases  are  so  important  that  we 
will  study  them  one  at  a  time.  Thus  you  see  that  the  air 
which  you  thought  was  just  one  thing  is  really  composed 
chiefly  of  four  substances:  nitrogen,  oxygen,  carbon 
dioxide,  and  water.  Besides  these,  there  are  argon,  dust, 
and  bacteria. 

Experiment  38. — The  Amount  of  Oxygen  in  the  Air. 
Apparatus:     Saucer,  glass,  candle,  flat  cork  stopper. 

a.  Cut  the  can- 
dle so  that  it  is 
not  more  than  one 
inch  long  and 
make  a  "life  pre- 
server" for  it  from 
the  stopper.  To  do 
this,  cut  a  round 
hole  in  the  stop- 
per, in  which  the 
candle  will  fit 
tightly.  The  cork 


CARBON  DIOXIDE  77 

need  be  only  one-fourth  of  an  inch  thick,  but  it  should  be 
placed  near  the  wick  end  of  the  candle.  Fill  the  saucer 
with  water,  place  the  candle  upon  the  water,  light  it,  and 
cover  with  the  glass.  Tell  what  happens. 

b.  How  high  did  the  water  rise?  The  candle  has 
used  all  of  the  oxygen  and  left  the  nitrogen.  How  much 
of  the  air  is  nitrogen  and  how  much  is  oxygen,  according 
to  your  experiment?  Why  did  not  the  candle  go  out  at 
once?  Why  did  not  the  water  begin  to  rise  when  the 
candle  was  covered?  Before  answering  this  question 
you  must  think  of  the  effect  of  heat  upon  a  gas.  See 
Experiment  24.  Why  did  the  water  continue  to  rise 
after  the  candle  went  out? 

Note : — The  same  experiment  may  be  repeated  with 
a  large  bottle,  having  straight  sides,  and  a  cake  pan,    or 
bread  pan,  to  see  if  the  same  results  will  be  ob- 
tained. 
The  following  experiment  is  for  the  teacher: 

Experiment  39. — The  Amount  of  Carbon  Diox- 
ide in  the  Air. 

Apparatus :  A  twenty-ounce  glass-stoppered 
bottle,  glass  measure  graduated  in  cubic  centi- 
meters, medicine  dropper  graduated  to  hold  one- 
third  of  a  cubic  centimeter. 

Materials:  Limewater  solution  (pure  water 
left  in  contact  with  slaked  lime  until  the  water 
will  not  take  up  any  more  lime.  Dilute  the  clear 
decanted  liquid  with  99  times  its  own  volume), 
phenolphthalein  solution  (dissolve  one  part  ot 
phenolphthalein  in  500  times  its  own  weight  of  50 
per  cent  alcohol.) 


78  AIR 

a.  Fill  bottle  with  pure  water,  and  empty  it  in  the 
place  where  the  air  is  to  be  tested.  This  will  insure  the 
bottle  being  filled  entirely  with  the  air  of  the  room.  Add 
10  c.  c.  of  limewater  solution  and  one-third  c.  c.  of 
phenolphthalein  solution,  stopper,  and  shake.  If  the  red 
color  disappears  in  three  minutes  or  less,  the  air  is  unfit 
to  breathe. 

30.     Oxygen  and  its  Uses. 

We  have  learned  that  air  is  necessary  for  life  of  any 
kind  and  that  it  is  composed  of  nitrogen,  oxygen,  carbon 
dioxide  and  water.  We  have  also  learned  that  it  is  the 
oxygen  which  caused  the  candle  to  burn  since  it  stopped 
burning  when  all  the  oxygen  had  been  used.  Therefore 
we  call  oxygen  the  supporter  of  combustion.  Just  as  the 
candle  needs  oxygen  in  order  to  burn,  so  we  need  oxygen 
in  order  to  live.  It  it  only  the  oxygen  of  the  air  which 
the  body  uses ;  the  nitrogen  is  exhaled  unchanged.  If 
there  are  many  persons  in  a  close  room  most  of  the  oxy- 
gen will  soon  be  used  and  the  air  will  become  unfit  for 
breathing.  Headaches  and  drowziness  are  more  often 
produced  by  bad  air  than  by  hard  lessons.  Yawning  is 
caused, by  a  desire  to  obtain  more  oxygen. 

Since  it  is  the  oxygen  of  the  air  which  supports  com- 
bustion and  air  is  composed  of  only  one-fifth  oxygen,  we 
might  suspect  that  combustibles  would  burn  much  more 
vigorously  in  oxygen  than  air.  Let  us  see  if  this  is  true. 

Experiment  40. — To  Prepare  and  Use  Oxygen. 
Apparatus:     Test  tube,  test-tube  holder,  burner. 


THE  PREPARATION  OF  OXYGEN  79 

Materials:  Potassium  chlorate  (powdered),  manga- 
nese dioxide,  splinters  of  wood. 

a.  Mix  equal  parts  of  potassium  chlorate  and  man- 
ganese dioxide  on  a  piece  of  paper,  and  pour  into  a  test 
tube.  Hold  the  test  tube  in  the  flame  of  the  burner,  by 
means  of  the  test-tube  holder,  until  it  becomes  very  hot. 
Then  light  a  splinter  of  wood,  let  burn  for  a  while,  blow 
out  the  flame,  and  insert  the  glowing  end  into  the  tube, 
continuing  to  heat  the  tube.  What  happens?  There  is  oxy- 
gen coming  from  the  mixture  in  the  tube.  Does  wood 
burn  better  in  oxygen  than  in  air?  Is  oxygen  invisible  or 
visible?  Colored  or  colorless? 

Review  Question,  17. 

1.  Why  does  the  skin  become  tanned? 

2.  If  you  run  toward  your  image  in  a  mirror  going 
ten  feet  a  second,  how  fast  will  you  approach  your  image? 

3.  How  should  the  lights  of  a  house  be  arranged  to 
give  the  best  light  for  the  eyes? 

4.  Why  are  woolen  underclothes  better  protection 
from  cold  than  cotton  garments? 

5.  Should  the  thermometer  hang  near  the  floor,  on 
the  level  of  your  head,  or  near  the  ceiling  of  a  room  to  be 
of  use  to  us? 

6.  How  can  you  show  that  there  is  air  in  water? 

7.  Give  all  the  reasons  which  make  you  think  that 
there  is  water  in  the  air. 

8.  How  can  you  show  that  about  four-fifths  of  the 
air  is  nitrogen? 

9.  Why    does    pure    oxygen     support    combustion 
better  than  air? 

10.  What  is  one  cause  of  headaches? 


AIR 


31.     Nitrogen  and  its  Uses. 

As  we  have  learned,  about  four-fifth  of  the  air  is 
nitrogen.  We  saw  that  it  was  oxygen  which  supported 
combustion  and  that  pure  oxygen  supported  combustion 
much  more  vigorously  than  air,  because  air  is  only  one- 
fifth  oxygen.  What  do  you  think  the  effect  would  be 
upon  fires  if  all  of  the  air  were  oxygen?  One  of  the  uses 
of  nitrogen,  then,  is  to  lessen  the  effect  of  oxygen.  Where 
the  amount  of  one  substance  is  reduced  by  the  addition 
of  another  we  say  that  the  first  substance  is  diluted,  and 
call  the  process  dilution.  Nitrogen  dilutes  the  oxygen. 
Pure  oxygen  is  sometimes  inhaled,  under  the  advice  of  a 
doctor,  by  those  who  have  weak  lungs. 

For  a  long  time  it  was  thought  that  nitrogen  hid  no 
other  use  than  to  dilute  the  oxygen.  Now  it  is  known 
that  tiny  plants,  so  small  that  they  are  invisible,  called 
bacteria,  live  upon  the  roots  of  some  of  the  larger  plants 
and  absorb  the  nitrogen  from  the  air.  This  they  change 
into  material  which  is  needed  by  the  larger  plants.  This 


Cut    supplied   through    United    States  Department  of  Agriculture. 


CARBON  DIOXIDE  81 

is  one  example  of  the  good  which  bacteria  do  for  us. 
Later  we  shall  learn  that  they  help  us  in  many  ways. 
The  larger  plants  cannot  take  in  the  nitrogen  until  it 
has  been  changed  by  the  bacteria,  and  many  of  the  plants 
could  not  live  if  it  were  not  for  the  bacteria. 

The  little  lumps  upon  the  roots  of  the  plant  in  the 
illustration  are  called  nodules.  Each  nodule  is  the 
home  of  bacteria.  The  illustration  is  the  root  of  the 
garden-pea,  but  there  are  nodules  upon  the  roots 
of  many  other  plants  and  trees.  Whenever  you  see  these 
nodules  you  will  know  that  there  are  many  helpful 
bacteria  within  them. 

The  kind  of  food  which  the  plants    form  from    the 
material  supplied  by  the  bacteria    is  the  source    of    our 
strength.     When  we  study  plants  and  food  we  shall  learn 
more  about  these  bacteria  and  their  work. 
32.     Carbon  Dioxide. 

The  amount  of  carbon  dioxide  in  the  air  varies 
according  to  the  location.  Near  factories  there  is  a  larger 
amount  than  in  the  open  country,  or  on  the  ocean,  while 
in  a  room  where  there  are  many  persons  the  amount  may 
become  very  great.  This  shows  that  fires  produce  it  and 
animals  exhale  it.  In  the  open  country,  air  contains 
only  three  or  four  parts  of  carbon  dioxide  in  ten  thousand 
parts.  The  gas  is  a  combination  of  oxygen  and  carbon. 
Coal,  coke,  and  charcoal,  all  of  which  are  fuels,  are  chiefly 
carbon.  If  the  air  of  the  room  contains  eight  to  ten  parts 
of  carbon  dioxide  in  ten  thousand  parts  of  air  it  is  unfit 
for  us  to  breathe.  Since  exhaled  air  contains  four  hun- 
dred parts  in  ten  thousand,  it  can  easily  be  seen  that  there 
should  be,  not  only  a  supply  of  fresh  air,  but  the  stale  air 
should  be  removed  continually.  In  addition  to  carbon 

Elem.  Sci.  6 


82  AIR 

dioxide  we  exhale  small,  invisible  particles  of  decayed 
animal  matter  which  also  are  poisonous  unless  diluted 
with  plenty  of  fresh  air.  You  all  know  the  story  of  the 
Black  Hole  of  Calcutta,  and  the  fatal  results  from  the  lack 
of  fresh  air. 

Carbon  dioxide  has  its  use  and  it  is  a  most  important 
one.  Plants  absorb  it  and  break  it  up  into  its  parts,  car- 
bon and  oxygen.  The  plants  keep  the  carbon,  making- 
wood  of  it,  and  give  out  the  oxygen  to  the  air  again. 
Thus  plants  purify  the  air.  For  that  reason  we  should 
have  plants  in  our  school  rooms  and  houses.  Plants  owe 
their  ability  to  take  in  carbon  dioxide  to  the  green  color- 
ing matter  in  their  leaves  and  stalks.  We  have  learned 
that  the  sunlight  causes  plants  to  be  green,  and  so  you 
see  that  it  is  the  sun  which  causes  plants  to  grow.  That 
is  why  plants  grow  in  the  direction  of  the  sun. 

Experiment  41. — Carbon  Dioxide  from  Combustion 
and  from  the  Breath. 

Apparatus:  Candle,  funnel,  syringe  bulb,  glass  tube, 
10"  long,  test  tube. 

Materials:  Limewater  (all  the  slaked  lime  that  will 
dissolve  in  water ;  use  the  clear  liquid  only.) 

a.  Arrange  apparatus  as  shown  in  the  illustration, 
light  candle,  and  force  the  gases  which  come  from  the 
candle  into  the  limewater.        What    happens?        What 
caused  the  change? 

b.  Blow  out  candle  and  repeat.     In  this  case  it  is 
the  air  of  the  room  which  is  being  forced  into  the  lime- 
water.     Does  the  change  take  place? 

c.  Take  the  apparatus   out  of  doors  and  repeat.     Do 


SOURCES  OF  CARBON  DIOXIDE 


83 


you  finally  see  any  change? 

d.  Now  repeat  (b.)  and  (c.),  counting  the  number 
of  times  it  is  necessary  to  squeeze  the  bulb  in  order  to 
obtain  the  same  result.  Divide  the  number  of  times  it 
takes  indoors  by  the  number  of  times  required  out  of 
doors.  The  result  will  show  about  how  much  more  car- 
bon dioxide  there  is  indoors  than  out  of  doors.  If  the 
room  is  properly  ventilated  there  should  be  little  differ- 
ence. Is  the  schoolroom  properly  ventilated? 


84 


AIR 


e.  Blow  through  the  glass  tube  into  some  limewater. 
Do  you  think  that  you  exhale  the  same  gas  as  a  candle 
produces? 


The  illustration  shows  a  method  of  collecting  the 
oxygen  which  is  given  off  by  a  plant.  In  this  case  it 
must  be  a  water  plant,  but  oxygen  is  given  off  by  all 
green  plants.  If  you  wish  to  perform  this  experiment  yon 
must  collect  some  water  plants  and  place  them  in  the 
bottom  of  a  large  dish.  Cover  them  with  a  funnel, 
which  must  be  of  glass,  and  fill  the  dish  until  the  top 
of  the  funnel  is  covered  with  water  to  a  depth  of. one 
inch.  Take  a  test  tube,  fill  it  with  water,  cover  the  end 
with  your  thumb,  and  invert  it  in  the  dish,  not  letting 

any  water  escape.  Slide  the 
test  tube  over  the  end  of 
the  funnel  and  set  the  whole 
apparatus  in  the  bright  sun- 
shine. In  a  few  minutes  you 
will  see  bubbles  forming, 
and  in  a  day  or  two,  the  test 
tube  will  contain  enough 
oxygen  for  a  test.  To  remove 
the  test  tube  lift  it  from  the 
funnel,  putting  your  thumb 
again  over  its  mouth,  while 
it  is  under  the  water,  and  re- 
move from  the  water.  Turn 
the  test  tube  right  side  up. 


RESPIRATION  85 

keeping  the  thumb  tightly  in  place.       Test  for    oxygen. 
How  will  you  do  it?    Is  it  oxygen?    How  do  you  know? 

33.     Respiration.     The  Necessity  for  Pure  Air. 

Breathing  consists  of  inhaling  and  exhaling.  Breath- 
ing is  also  called  respiration.  Do  you  know  how  many 
breaths  you  take  in  a  minute?  How  can  you  find  out? 
Do  you  always  take  the  same  number  of  breaths  in  a 
minute?  What  makes  you  breathe  faster  sometimes? 
Your  heart  beats  faster  when  you  breathe  faster.  A 
grown  person,  or  adult,  breathes  18  times  a  minute,  not 
exercising,  and  his  heart  beats  72  times  a  minute,  or  four 
times  the  number  of  breaths.  Young  persons  breathe 
faster  and  their  hearts  beat  faster.  Usually  the  heart 
beats  four  times  for  each  breath. 

We  should  breathe  through  our  nose  because  it  is  a 
sort  of  sieve  which  keeps  the  dust  from  passing  on  to  the 
lungs,  and  it  also  warms  the  air  a  little  before  it  reaches 
our  lungs.  If  persons  find  trouble  in  breathing  through 
the  nose  they  should  consult  a  doctor. 

The  amount  of  air  which  we  ordinarily  inhale  and 
exhale  at  each  breath  is  30  cubic  inches.  When  we  draw 
a  long  breath,  or  "heave  a  sigh,"  the  quantity  of  air 
which  we  inhale  or  exhale  is  about  130  cubic  inches.  By 
trying,  we  can  exhale  about  100  cubic  inches  more.  Even 
then  there  remains  about  100  cubic  inches  which  cannot 
be  exhaled.  The  amount  of  air  which  the  lungs  hold  is 
called  their  capacity.  All  persons  do  not  have  the  same 
lung  capacity,  but  where  the  capacity  is  less  than  it 
should  be,  it  may  be  increased  by  breathing  exercises  and 
the  right  kind  of  physical  exercise. 


86  AIR 

Experiment  42. — The  Capacity  of  the  Lungs. 

Apparatus:  Large  bottle,  holding  at  least  a  gallon, 
cork  stopper  to  fit,  large  pan,  holding  at  least  two  gallons, 
piece  of  rubber  tubing  three  feet  long,  piece  of  glass 
tubing  which  has  had  its  rough  edges  rounded  off  in  a 
flame. 

a.  Fill  the  bottle  full  of  water,  insert  the  stopper 
and  invert  in  a  pan  in  which  there  is  about  two  quarts  of 
water.  Remove  the  stopper  and  slip  one  end  of  the 
rubber  tubing  up  into  the  bottle,  which  should  be  tipped 
a  little  to  one  side,  and  held  there,  in  order  not  to  jam  the 
tubing.  The  glass  tubing  should  be  inserted  in  the  other 
end  of  the  rubber  tubing  to  serve  for  a  mouthpiece,  which 
may  be  washed  before  each  pupil  uses  it.  Take  several 
long  breaths  before  measuring  your  lung  capacity.  Then 
take  the  longest  breath  possible,  place  the  tube  in  the 
mouth,  and  blow  hard.  Keep  on  blowing  until  you  can- 
not exhale  a  bubble  more.  Immediately  remove  the 
rubber  tube  from  the  bottle  and  estimate  your  lung 
capacity.  There  are  231  cubic  inches  in  a  gallon.  If 
100  cubic  inches  of  air  still  remained  in  your  lungs,  what 
is  the  capacity  of  your  lungs? 


The  amount  of  air  which  is  needed  per  minute,  in  a 
room  in  which  there  are  several  persons,  cannot  be  found 
out  by  multiplying  the  number  of  cubic  inches  used  in 
each  breath  by  the  number  of  breaths  per  minute,  and 
by  the  number  of  persons  in  the  room.  We  must  remem- 
ber that  the  air  which  we  exhale  contains  four  hundred 
parts  of  carbon  dioxide  in  ten  thousand,  while  the  proper 


THE  NECESSITY  FOR  TURE  AIR  87 

amount  of  carbon  dioxide  is  no  more  than  eight  or  ten 
parts  in  ten  thousand.  Now  400  is  50  times  8.  This 
means  that  one  breath  spoils  50  times  that  amount  of  air, 
not  only  for  others  but  even  for  ourselves.  For  this 
reason  it  is  very  necssary  to  have  a  large  supply  of  fresh 
air.  If  there  are  lights  burning  in  the  room,  such  as 
kerosene  lamps  or  gas,  much  more  air  is  needed.  An 
ordinary  light  spoils  as  much  air  as  four  persons  in  the 
same  time.  Electric  light  does  not  affect  the  air. 

Review  Questions,  18. 

1.  Why  does  pouring  hot  water  into  a  glass  dish 
break  it?       Would  there  be  any  difference  if  the  glass 
were  thin? 

2.  What  is   the   result  of  incomplete    combustion? 
Why  is  it  not  wise  to  allow  incomplete  combustion? 

3.  Why  should  a  person  not  run  if  his  clothing  is  on 
fire?     What  should  he  do  if  he  is  alone? 

4.  What  kind  of  clothing  is  most  liable  to  burn? 

5.  What  is  the  composition  of  the  air? 

6.  What  would  happen  if  there  were  no  nitrogen? 

7.  How  does  carbon  dioxide  get  into  the  air? 

8.  At  the  ordinary  rate  of  breathing,  how  much  air 
will  twenty  pupils  breathe  in  half  an  hour?     How  much 
air  will  they  spoil  in  the  same  time? 

9.  Find  the  number  of  cubic  inches  of  air  in    your 
schoolroom  and  tell  how  many  times  it  must  be  changed 
in  every  half  hour  in  order  to  give  you  enough  fresh  air, 
if  you  were  the  only  person  in  the  room. 

10.  Solve  Problem  9  for  the  number  of  persons  in 
Tour  room. 


THE  GUIDE 


WATER. 

34.     Water  is  a  Liquid. 

A  block  of  wood,  or  a  stone,  has  a  shape  which  does 
not  change.  What  is  the  shape  of  a  quart  of  water? 
Water  will  fit  any  dish  that  you  put  it  into,  and  thus  has 
no  shape  of  its  own.  Anything  which  has  a  shape  which 
does  not  change  is  called  a  solid.  If  the  material  fits  the 
dish  into  which  it  is  put  and  leaves  no  empty  spaces,  it 
is  a  liquid. 

While  water  is  a  liquid  and  fits  perfectly  every  dish 
into  which  it  may  be  put,  there  is  one  part  which  is 
always  the  same.  This  is  the  top  of  the  water,  called  its 
surface.  The  surface  of  water  is  always  flat,  or  hori- 
zontal. Another  name  for  horizontal,  is  level.  All 
parts  of  a  horizontal,  or  a  level  line  are  the  same  distance 
from  the  center  of  the  earth.  If  we  want  to  make  the 
floor  of  a  house  level  we  can  do  so  by  means  of  a  hori- 
zontal surface  of  water. 

Experiment  43. — The  Level. 

Apparatus:     Pie  tin,  small  round  bottle  and  stopple. 

a.  Half  fill  the  pie  tin  with  water  and  place  it  upon 
the  board  which  you  are  to  make  level.  If  the  water 
does  not  come  up  the  same  distance  all  around  the  tin, 
when  it  is  on  the  board,  the  board  is  not  level,  or  hori- 
zontal. Put  little  pieces  of  wood  or  stones,  under  the 
low  sides  of  the  board  until  the  water  is  at  the  same 
height  all  around  the  tin.  Can  a  board  be  horizontal  in 
one  direction,  say  north  and  south,  and  not  horizontal  in 


90  WATER 

the  east  and  west  directions?       Is  there  any    difference 
between  being  level  and  being  horizontal? 

b.  Half  fill  the  little  bottle  with  water  and  lay  it 
upon  its  side  on  a  board.  When  the  surface  of  the  water 
is  the  same  distance  up  from  the  side  of  the  bottle,  all 
along,  the  board  is  horizontal  in  the  direction  of  the 
length  of  the  bottle.  How  can  you  make  a  board  level  by 

means  of  the  bottle? 
The  bottle  is  called  a 
level.  A  simple  level 
is  shown  in  the  illustra- 
tion. In  this  level  the 
tube  is  curved  so  that  the  air  bubble  is  always  at  the 
highest  part. 


A  block  of  wood,  or  a  stone,  will  stay  where  you  put 
it;  water  will  run  off.  All  liquids  act  in  the  same  manner 
and  are  said  to  flow.  If  the  water  faucet  is  gradually 
shut  so  that  the  Pow  of  water  becomes  less  and  less,  the 
stream  will  suddenly  break  into  drops.  How  would  a 
rainstorm  be  if  water  did  not  break  into  drops?  Water- 
drops  are  all  the  same  size  unless  the  drops  come  together. 
Do  raindrops  ever  come  together? 

On  account  of  the  flowing  of  water  there  is  a  saying, 
"Water  always  seeks  its  own  level."  This  means  that 
the  surface  of  water  is  at  the  same  level  everywhere  if 
the  water  can  flow  freely  between  all  parts. 

Experiment  44. — *Water  Seeks  its  own  Level.  Size 
of  Drops. 


*  It  is  desirable  to  take  Sec.  58  before  performing  this  experiment. 


WATER  SEEKS  ITS  OWN  LEVEL 


91 


Apparatus:  Funnel,  rubber  tubing,  glass  tube  to 
make  apparatus  as  shown  in  the  illustration,  medicine 
dropper,  graduate  (50  c.  c.),  small  dish. 

Fill  the  funnel  and  tube  with  water  and  hold  the 


a. 


funnel  and  tube  in  various  positions.  What  do  you 
notice  in  regard  to  the  level  of  the  water  in  the  funnel 
and  the  level  of  the  water  in  the  tube? 

b.  Fill  the  medicine  dropper  and  carefully  count 
the  drops  which  are  needed  to  make  5  cubic  centimeters. 
In  reading  the  graduate  it  must  be  placed  on  a  level  table 
and  the  reading  must  be  taken  with  the  eye  on  a  level 
with  the  surface  of  the  water.  Read  the  lower  surface 
of  the  water.  How  many  drops  in  one  cubic  centimeter? 
If  there  are  946  cubic  centimeters  in  a  quart,  how  many 
drops  of  water  are  there  in  a  quart? 

35.     Water  can  Pass  into  Some  Things. 

If  we  put  a  sponge  into  water  some  of  the  water 
goes  into  the  sponge.  The  same  thing  is  true  of  clothing. 


92  WATER 

We  know  that  if  we  step  into  water  it  soaks  into  and 
through  our  shoes.  All  bodies  which  allow  water  to  pass 
into  them  or  through  them  are  called  porous,  on  account 
of  many  little  holes  in  them  which  are  called  pores. 
When  porous  bodies  take  in  water  we  say  that  they 
absorb  water.  There  are  other  bodies  which  are  porous 
although  they  do  not  seem  to  be  so  unless  we  experiment 
with  them.  A  brick  is  very  porous,  and  so  are  many 
rocks.  As  you  know,  the  ground  is  porous,  or  the  rain 
would  not  sink  into  it. 

Experiment  45. — *Porous   Bodies   Absorb   Water. 
Apparatus:     Balance,  weights,  cake  pan. 
Materials:     Sponge,  cloth,  brick,  porous  stone. 

a.  Weigh  the  sponge  dry,  let  it  soak  in  water   and 
weigh  again.     What  is  the  gain  in  weight?     How  much 
water  could  a  pound  of  sponge  take  in? 

b.  Repeat  with  the  brick.     The  brick  should  remain 
in  the  water  for  a  full  day. 

c.  Repeat  with  the  cloth  and  porous  stone. 


The  only  reason  that  some  bodies  are  porous  is 
because  they  contain  little  holes,  or  pores.  If  we  wish 
to  keep  the  water  out  of  a  body  we  must  close  the  holes, 
just  as  we  close  the  gate  to  keep  out  the  dogs  or  other 
animals.  Preparing  material  so  that  it  will  not  permit 
water  to  enter  is  called  waterproofing.  See  Section  74. 

Experiment  46. — To  Make  Porous  Bodies  Water- 
proof. 

*  Section  59  should  precede  this  experiment. 


WATERPROOFING  93 

Apparatus:  Burner,  ring  stand,  wire  gauze,  tin 
dish. 

Materials:     Piece  of  cloth,  4"x5",  paraffin. 

a.  Melt  the  paraffin  by  gentle  heat  and  dip  the 
cloth  into  it.  While  the  paraffin  on  the  cloth  is  still 
warm,  shape  the  cloth  into  a  four-sided  box.  When  cold 
it  should  hold  water.  What  keeps  the  water  from  going 
through  the  cloth? 

Rubber  is  the  material  which  is  commonly  used  to 
fill  the  pores  of  porous  material,  in  order  to  make  it 
waterproof,  as  rubber  is  not  altered  by  ordinary  changes 
in  temperature.  Do  you  think  that  your  box  would 
hold  hot  water? 


While  it  is  not  pleasant  to  have  water  come  through 
our  clothing  or  even  our  houses,  the  porosity  of  materials 
has  its  use.  Water  which  passes  through  the  small  pores 
has  lost  a  large  amount  of  its  dirt.  The  separation  of 
dirt  from  water,  by  means  of  porous  bodies,  is  called 
filtration,  and  the  porous  body  is  called  a  filter.  All 
water  which  comes  from  the  earth  in  springs  and  wells 
has  been  filtered  by  passing  through  the  porous  ground. 
We  can  filter  water,  where  necessary,  by  means  of  porous 
dishes  or  porous  paper. 

Experiment  47. — Filtration. 

Apparatus:  Funnel,  funnel-holder  (cut  a  hole  in  the 
small  end  of  a  chalk  box),  test  tubes. 


94  WATER 

Materials:     Sawdust,  sand,  filter  paper. 

a.  To  use  filter  paper,  fold  it 
in  halves  and  then  again  in  quar- 
ters, as  shown  in  the  illustration. 
Separate  one  thickness  from  the 
other  three  and  place  in  funnel. 
Mix  some  sawdust,  sand  and 
water.  Then  filter.  Does  the 
water  pass  through  clear? 

Review  Questions,  19. 

1.  What  are  two  causes  of  the  variation  in  the  heat 
which  we  receive  from  the  sun? 

2.  What  causes  contraction? 

3.  What  part  of  the  room  is  the  warmest,  near  the 
ceiling,  on  the  level  of  your  head,  or  near  the  floor? 

4.  What  are   the   advantages    of    deep    breathing? 
How  can  you  prove  your  answer  by  figures? 

5.  Name  the  parts  of  the  air  that  are  used  by  plants, 
stating  how  they  are  used,  and  the  parts  of  the  air  which 
are  taken  in  by  animals,  giving  the  use  of  each  part. 

6.  If  you  were  given  a    long    rubber    tube,    which 
would  reach  across  the  room,  and  two  glass  tubes  to  fit 
the  ends  of  the  rubber  tube,  tell  how  you  could  put  two 
shelves  on  the  opposite  sides  of  the  room  at  exactly    the 
same  level. 

7.  How  could  you  find  out  whether  a  body  is  porous? 

8.  Name  all  of  the  porous  bodies  you  can  think  of 
and  state  the  advantages  or  disadvantages  which  are  due 
to  their  porosity. 

.     9.     What  is  meant  by  waterproofing.       Give  some 
examples  of  waterproofing. 


SOLUTION 


95 


10.  Why  is  water  from  springs  usually  clear,  while 
water  in  rivers  is  dirty? 

36.     Solution. 

When  we  put  sand  or  sawdust  into  water  we  could 
still  see  it.  Can  you  see  sugar  when  you  have  put  a  little 
into  water  and  have  stirred  it  well?  If  a  solid  disappears, 
when  put  into  a  liquid,  we  say  that  the  solid  dissolves, 
and  we  call  the  result  a  solution.  Not  only  does  water 
dissolve  solids  but  it  can  also  hold  gases  in  solution. 
Any  liquid  which  can  dissolve  solids  or  gases  is  called  a 
solvent.  In  Section  28  we  saw  that  water  can  hold  con- 
siderable air  in  solution  if  the  water  were  cold.  The  best 
way  to  learn  more  about  solution  is  by  experimenting. 

Experiment  48. — Solution  and  its  .Oddities. 

Apparatus:  Two  glasses,  tin  spoon,  burner,  tin 
cans,  thermometer,  funnel,  filter  paper,  glass  rod. 

Materials :  Sugar,  salt,  baking  soda,  cream  of  tar- 
tar, ammonium  chloride  (commonly  called  sal  ammoniac). 

a  Fill  a  glass  full  of  water.  Very  slowly  add 
some  sugar  while  carefully  stir- 
ring. Note  that  it  is  possible  to 
add  considerable  sugar  without 
making  the  water  overflow.  Now 
add  some  salt  in  the  same  way 
to  the  same  water.  Can  you  do 
it  without  making  the  water 
overflow?  What  is  one  of  the 
oddities  of  solution?  Try  filter- 
ing the  solution.  Do  the  sugar 
and  the  salt  pass  through?  The 
method  of  pouring  liquids  from  a 
glass  is  shown  in  the  illustration. 


96  WATER 

b.  Put  a  little  cold  water  in  one  glass  and   the  same 
amount  of  hot  water  in  another  glass.       Now  see  how 
much  sugar  will  dissolve  in  the  cold  water  and  how  much 
in  the  hot  water.     When  a  solvent  holds  all  of  a  solid  it 
can,  the  solution  is  said  to  be  saturated  for  that  temper- 
ature.    Which  solution  becomes  saturated  first,  the  hot 
one  or  the  cold  one?       Which  is  better    for    dissolving 
solids,  cold  water  or  hot  water? 

c.  Fill  a  glass  one-fourth  full  of  cold  water,  take  its 
temperature,  and  then  add  half  as  much  sal  ammoniac  ^ 
there  is  water.     Stir  rapidly  and  immediately    take    its 
temperature.     What  is  another  oddity  of  solution?     Can 
you  explain   (b.)   above,  now  that  you  have  done   (c.)  ? 
Do  you  think  that  the  solution  is  saturated?     Why? 

d.  Put  a  little  dry  baking  soda  and    a    little    dry 
cream  of  tartar  into  a  dry  glass.     Nothing  will  happen. 
Now  add   some   water.     What   happens?     Solution   per- 
mits the  action  of  one  material  upon  the  other.       The 
gas  is   carbon   dioxide  and   it  is   this   gas   which    makes 
soda  biscuits  rise- 


Water  owes  its  power  of  removing  dirt  to  the  fact 
that  it  can  dissolve  so  many  substances,  but  there  are 
many  kinds  of  material  which  water  cannot  dissolve. 
Fortunately  for  us  there  are  other  solvents  which  can 
dissolve  some  of  these.  Two  common  examples  of  spe- 
cial solvents  are  alcohol  and  gasolene.  We  should  be 
very  careful  when  we  are  using  either  of  these  solvents. 


OTHER  SOLVENTS  97 

not  to  be  near  a  fire,  or  even  be  in  the  same  room  with  a 
fire  or  a  burning  lamp,,  for  both  are  very  easily  set  on  fire. 
Gasolene  produces  a  gas  which  may  be  set  on  fire  by  a 
flame  although  several  feet  away. 

Experiment  49. — *The  Use  of  Gasolene  and  Alcohol 
as  Solvents. 

Apparatus:     Two  small  bottles  with  stoppers. 

Materials:  Gasolene,  alcohol,  kerosene,  pieces  of 
cloth,  grease  (lard),  rosin,- pitch. 

a.  Shake  a  little  grease  with  water  in  a  bottle.  Does 
the  grease  dissolve  in  the  water?     Pour  off  the  water,  add 
gasolene  and  shake  again.     What  is  the  result? 

b.  Put  a  very  little  grease  on  a  piece  of  cloth.    This 
will  make  a  grease  spot.     To  remove  the  grease  spot  the 
space  all  around  the  spot  should  be  wet  with  gasolene 
before  putting  the  gasolene    upon    the    spot    itself.       If 
gasolene  is  put  upon   the    grease  first  the    grease    will 
spread  and  leave  a  ring  after  the  spot  has  been  removed. 
Try  putting  the  gasolene  upon  a  grease  spot  on  a  second 
piece  of  cloth  and    notice    the    familiar    ring    when    the 
gasolene  has  evaporated. 

c.  Shake  ?  Httle  powdered  rosin  witb  water  in  a  bot- 
tle. Does  the  water  dissolve  the  rosin?  Pour  off  the  water, 
add  some  alcohol,  and  shake  again.     What  is  the  effect  of 
alcohol  upon  the  rosin?     Pour  the  result  upon  a  smooth 
piece  of  wood  and  allow  the  alcohol  to  evaporate  undis- 
turbed.    How  does  the  wood  appear?     Rosin  is  used  in 
cheap  varnishes.     Do  the  cheap  varnishes  scratch  easily? 

d.  Put  some  pitch  upon  a  piece  of  cloth  and  remove 

*     This  experiment  may  be  omitted  or  performed  only  by 
the  teacher. 

Elem.  Sci.  7 


98  WATER 

it  with  kerosene.  It  may  be  necessary  to  allow  the  cloth 
to  soak  in  the  kerosene  for  some. time.  Pitch  may  be 
removed  from  the  hands  with  kerosene.  The  kerosene 
may  then  be  removed  with  soap  and  water. 

37.     Crystals. 

We  have  seen  that  some  solids  can  disappear  in 
solution.  Do  you  think  that  they  can  come  out  of  solu- 
tion and  appear  again?  The  only  way  in  which  we  can  get 
a  solid  out  of  solution  is  to  drive  off  the  water  by  means 
of  heat,  called  boiling,  or  we  can  let  the  water  pass  off 
slowly  and  without  bubbling.  This  last  method  is  called 
evaporation.  Let  us  learn  about  this  by  some  experi- 
ments. 

Experiment  50. — Crystallization. 

Apparatus:  Burner,  ring  stand,  wire  gauze,  two 
beakers,  three  glasses,  stirring  rod,  deep  dish. 

Materials:  Alum  (powdered),  copper  sulphate, 
common  salt,  string. 

a.  To  a  little  water  add  one  half  as  much  powdered 
alum  and  stir  for  a  few  minutes.  Does  it  all  dissolve? 
Now  put  it  on  the  ring  stand,  resting  it  upon  the  wire 
gauze,  and  heat  it  until  it  boils.  Does  heat  aid  solution? 
Place  the  beaker  containing  the  solution,  in  a  dish  of  cold 
water  and  stir  it  constantly  until  cold.  What  happens? 
Heat  the  beaker  again  until  all  of  the  alum  has  dis- 
solved and  then  place  it  again  in  the  dish  of  cold  water, 
but  do  not  stir  it  or  touch  it  until  it  is  cold.  What  is 
the  result?  What  you  see  are  crystals.  Which  method 
produces  the  larger  crystals,  rapid  cooling  or  slow  cool- 
ing? Keep  the  crystals. 


CRYSTALLIZATION 


99 


b.  Repeat  (a.),  using  the  same  amount  of  water  but 
using    three-fourth    as     much    copper 

sulphate  as  water,  in  the  place  of  alum. 
What  are  your  results?  Note  the 
shape  of  the  crystals.  Are  they  the 
same  as  the  alum  crystals?  A  micro- 
scope, such  as  is  shown  in  the  illu 
tration  will  help  you,  although  it  is  not  a  necessity. 

c.  Make  a  saturated  solution  of  common  salt,  one 
of  alum,  and  one  of  copper  sulphate.       Place  in  separate 
glasses  and  in  each  solution  hang  a  piece  of  string  from 
a  little  stick  placed  across  the  top  of  the  glasses.       Set 
aside  for  a  few  days.       The  water  will    evaporate    and 
leave  the  solids.       Are  all  the  crystals  the  same  shape? 
The  crystals  of  any  one  substance  are  always  the  same 
where  they  have  formed  slowly  and  have  had  plenty  of 
room  in  which  to  form.       Can  you    tell    the    difference 
between  a  salt  crystal  and  an  alum  crystal? 


There  are  many  crystals  in  nature  although  there 
are  but  six  different  kinds.  We  may  imitate  a  few  of  the 
crystals  by  cutting  out  the  shapes,  as  shown  in  the  illus- 


100  WATER 

trations,  from  thick  paper,  folding  on  the  dotted  lines, 
and  pasting  their  edges  together  by  means  of  strips  of 
paper. 

38.     Water  for  Drinking. 

There  is  hardly  any  pure  water  as  it  occurs  in  nature. 
On  account  of  the  great  power  which  water  has  to  dis- 
solve so  many  substances,  there  is  usually  some  material 
held  in  solution.  Fortunately  for  us,  many  of  the  sub- 
stances found  in  water  are  not  harmful  to  man,  while 
some  of  them  are  very  helpful.  The  harmful  substances 
which  are  dissolved  in  water  are  usually  so  bad  tasting 
that  there  is  little  danger  from  them,  for  no  one  will  drink 
the  water. 

While  the  dissolved  material  is  usually  harmless, 
there  is  great  danger  in  drinking  impure  water.  This  is 
due  to  a  kind  of  plant  life  we  have  already  become 
acquainted  with  in  Sections  13  and  25.  Some  of  these, 
which  we  learned  were  called  bacteria,  may  cause  typhoid 
fever.  Although  the  water  is  clear  and  seems  pure,  the 
bacteria  may  be  present.  On  the  other  hand,  dirty 
water  may  be  free  from  bacteria  and  be  harmless.  Wells 
should  be  so  located  that  drainage  cannot  possibly  reach 
them,  for  decayed  animal  matter  is  what  these  bacteria 
live  upon.  Since  water  can  pass  through  the  porous 
rocks,  wells  must  be  far  away  from  open  drains  and 
stables. 

The  body  requires  a  large  amount  of  water  and  most 
grown  persons  do  not  drink  enough.  The  more  water 
we  drink  the  better  are  the  wastes  carried  from  the  body. 
We  have  learned  that  while  water  can  dissolve  many 


DRINKING /"  :*.OJ*(i*'-i  l&} 

things,  a  limited  amount  of  water  can  dissolve  only  a 
limited  amount  of  any  one  solid.  Thus,  unless  we  drink 
a  sufficient  amount  of  water,  the  impurities  which  are 
produced  in  our  bodies  by  the  wear  and  tear  of  living,  or 
those  which  are  taken  in  with  food,  will  not  be  carried 
off  rapidly  enough.  Unless  we  are  warm  we  should 
drink  all  the  water  we  desire.  It  is  best  to  drink  slowly 
and  often,  rather  than  rapidly  and  in  large  quantities. 

While  the  drinking  of  a  large  amount  of  water  is 
very  desirable,  and  even  necessary,  yet  there  are  other 
common  drinks  which  are  harmful.  Any  drink  which 
contains  alcohol,  such  as  beer,  wines,  whiskey,  brandy, 
and  many  others,  cannot  fail  to  harm  a  person  to  some 
extent.  Alcohol  is  a  poison,  and  even  a  small  amount  of 
a  poison  will  have  some  harmful  effect.  Some  persons 
who  use  drinks  which  contain  alcohol  may  seem  to  be 
unaffected,  but  they  do  not  know  how  much  greater 
progress  they  might  have  made  if  they  had  left  alcohol 
alone.  Alcohol  should  always  be  considered  as  a  drug. 

Compared  with  alcohol,  coffee  and  tea  are  not  very 
harmful  to  grown  persons  unless  used  to  excess.  Young 
persons  should  not  drink  either  coffee  or  tea  until  they 
have  completed  their  growth.  Even  grown  persons 
should  be  careful  not  to  drink  too  much  of  either  coffee 
or  tea.  A  person  who  uses  too  much  of  these  drinks 
becomes  nervous  and  irritable,  and  his  eyes  are  often 
affected. 

Review  Questions,  20. 

1.  Why  is  it  warmer  in  summer  than  in  winter? 
Whv  is  it  warmer  near  noon  than  at  sunrise  or  sunset? 


V52,  i  JVH.J.P      WATER 

2.  If    your    clothing    should    be  set    on  fire,    what 
would  you  do.       What  would  you  do  if  you    saw    the 
clothing  of  another  person  burning? 

3.  Why  are  you  sure    that    there  must    be  air    in 
water? 

4.  How  much  air  does  a  person  spoil  by  breathing 
for  one  hour? 

5.  What  is  the  best    kind    of  light    to  use    in    our 
houses?     Why? 

6.  Why  are  brick  houses  sometimes  damp?     Could 
the  dampness  have  been  prevented? 

7.  Why  do  we  stir  or  beat  frosting  for  cake  for  a 
long  time?     If  we  did  not  beat  fudge  what  would  be  the 
result? 

8.  What  is  meant  by  evaporation?       What  causes 
evaporation  to  be  more  rapid? 

9.  When  do  we  need  the  more  water  for  drinking, 
when  we  have  been  perspiring  a  great  deal,  or  hardly 
perspiring  at  all? 

10.  Explain 'how    harmful    drinks    may   injure    us 
although  we  may  not  notice  the  effects. 

39.     Water  for  Cleansing. 

The  most  important  use  for  water  is  for  drinking. 
We  shall  see  in  the  next  section  that  plants,  as  well  as 
animals,  require  a  large  amount  of  water  in  order  to  live. 
The  use  for  water  which  is  next  in  importance  to  its  use 
for  drinking  and  for  plants,  is  its  use  for  cleansing.  Water 
owes  its  power  of  cleansing  to  its  ability  to  dissolve  so 
many  substances. 

We  know  that  if  water  has  some  dissolved  substance 


HARD  AND  SOFT  WATER          103 

already  in  solution  it  will  not  dissolve  other  substances 
as  readily  as  will  pure  water.  If  water  has  very  little 
dissolved  material  in  it,  it  will  cleanse  easily.  We  call 
such  water  soft.  Rain  water  which  has  fallen  after  it 
has  been  raining  for  some  time,  is  very  soft.  Why? 
Water  obtains  its  dissolved  .material  from  the  ground. 
Water  which  contains  dissolved  substances  is  called 
hard.  Soft  water  makes  suds  with  soap  very  easily 
while  hard  water  does  not.  Since  soap  has  the  power  of 
acting  with  the  water  to  dissolve  or  loosen  dirt,  if  it  does 
not  dissolve  in  the  water  and  form  suds,  the  water  is 
hard  to  use  for  washing.  Cleansing  is  much  easier  with 
soft  water  than  with  hard  water. 

Experiment  51. — *Hard  and  Soft  Water.     Soap. 

Apparatus:  Burner,  ring  stand,  tin  cup,  pint  bottle 
with  stopper. 

Materials:  Distilled  water,  powdered  or  shaved 
soap. 

a.  Measure  the  smallest  amount  of  soap  which  will 
just  begin  to  make  suds  when  shaken  with  a  half  pint 
of  distilled  water  in  a  pint  bottle.     This  will  give  you  a 
standard,  for  distilled  water  is  absolutely  pure  and  will 
make  suds  with  the  least  amount  of  soap.       Any  other 
water  will  use  more  soap. 

b.  See  how  much  soap  is  necessary  to  produce  suds 
with  a  half  pint  of  ordinary  water.       Take  another  "half 
pint  of  the  same  kind  of  water  which  has  been  boiled  for 
at  least  five  minutes.     Does  it  take  more  or  less  soap  to 
make  suds  with  the  boiled  water  than  with  the  unboiled 
water?     Hard  water  which  can  be  made  soft  by  boiling 

*    See   Experiment  79. — Distillation. 


104 


WATER 


is  called  temporarily  hard.  If  the  water  is  not  rendered 
soft  by  boiling  it  is  called  permanently  hard.  Was  the 
water  you  used  temporarily  or  permanently  hard,  or  was 
it  soft? 


Since  hard  water  requires  more  soap  than  soft  water, 
in  order  to  produce  suds,  the  use  of  hard  water  for  cleans- 
ing is  more  expensive  than  the  use 
of  soft  water.  Water  which  is  tem- 
porarily hard  contains  carbon  diox- 
ide, as  well  as  a  solid.  When  we 
boil  it  the  heat  drives  off  the  gas 
and  the  solid  collects  on  the  sides 
and  bottom  of  the  dish ;  thus  both 
are  removed  on  account  of  the  heat 
and  the  water  becomes  soft.  How 
could  you  show  that  carbon  diox- 
ide is  driven  off  from  temporarily  hard  water? 

We  wash  our  clothing  to  remove  the  visible  dirt  so 
that  the  clothing  will  be  neat  and  clean.  At  the  same 
time  we  remove  the  invisible  dirt  which  is  usually  more 
harmful  than  the  visible.  The  invisible  dirt  is  composed 
chiefly  of  material  which  has  been  left  by  the  perspira- 
tion when  it  evaporated,  particles  of  dead  skin  and 
bacteria.  Since  the  perspiration  comes  from  our  bodies 
it  is  of  great  importance  that  we  keep  our  skin  clean — 
not  alone  visibly  clean  but  really  free  from  anything 
which  can  be  washed  off.  The  mouths  of  the  tubes 
through  which  the  perspiration  comes,  called  pores. 


PLANTS  NEED  WATER  105 

should  be  kept  clean  and  open  by  frequent  baths  which 
ought  to  be  taken  daily,  if  possible. 

Dirt  cannot  be  removed  completely  without  the  use 
of  soap.  There  are  two  kinds  of  soap — laundry  soap  and 
toilet  soap.  Soap  which  is  suitable  for  washing  clothes 
and  for  general  housecleaning  is  usually  unfit  to  be  used 
on  the  skin.  On  the  other  hand,  toilet  soap,  which  is 
intended  for  tender  skin,  would  have  little  cleaning- 
power  if  used  on  clothes.  See  Section  77. 

40.     Plants  Need  Water. 

We  all  know  that  plants  need  water,  for  if  we  forget 
to  water  them  they  quickly  wilt,  and,  if  they  go  too  long 
without  water  they  die.  If  the  plants  have  only  wilted 
they  soon  take  up  the  water  and  become  stiff  and  vigor- 
ous again.  In  the  next  section  we  shall  learn  the  reason 
for  this  change.  The  amount  of  water  which  plants 
need  is  very  great.  The  water  is  carried  away  from  the 
leaves  by  evaporation,] ust  as  it  is  carried  from  wet  clothes 
which  are  hung  to  dry.  When  we  think  of  the  very 
large  surface  of  the  leaves  of  a  tree  we  will  realize  that 
the  amount  of  water  which  can  be  given  off  is  enormous. 
We  call  the  giving  off  of  water  from  the  leaves  of  a 
plant  transpiration.  Transpiration  takes  place  only  on 
the  under  side  of  leaves. 

Seeds  will  not  begin  to  open  unless  they  are  supplied 
with  water.  Then  they  swell  until  they  burst,  and  the 
young  plant  comes  forth.  The  amount  that  seeds  swell 
is  always  a  surprise,  as  you  know  if  you  have  ever  "put 
beans  to  soak." 


106 


WATER 


Experiment  52. — The  Effect  of  Water  upon  Seeds 
and  Plants. 

Apparatus:  Two  glasses  large  enough  to  cover  a 
small  plant. 

Materials:  Beans,  a  plant  in  a  can  or  pot,  two 
pieces  of  cardboard  6"x6". 

a.  Fill  a  glass  one-half  full  of  beans  and  then  com- 
pletely fill  the  glass  with  water.  Set  aside  for  twenty-four 
hours  and  tell  what  happened.  The  beans  may  be  dried 
by  putting  them  in  the  sun. 

b.  Cut  a  slit  in  each 
piece  of  cardboard  from  the 
middle  of  one  side  to  the 
center.  Slip  the  pieces 
around  the  stem  of  the 
plant  from  opposite  sides 
and  press  them  down  upon 
the  top  of  the  flower-pot. 
Cover  the  plant  with  the 
glass  and  set  it  in  the  sun. 
The  experiment  should  ap- 
pear like  the  illustration. 
What  collects  on  the  glass 
after  an  hour  or  so? 
Where  does  it  come  from  ? 
Why  were  the  pieces  of  cardboard  used? 

41.     Capillarity. 

The  word  "capillary"  means  "like  a  hair,"  that  is., 
very  fine.  Capillarity  is  the  strange  action  of  liquids  in 


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CAPILLARITY  107 

tubes  which  are  as  fine  as  a  hair,  or  even  finer.  Let  us 
perform  some  experiments  which  show  capillarity  and 
talk  about  it  afterwards. 

Experiment  53. — Examples  of  Capillarity. 

Apparatus:  Several  6"  pieces  of  glass  tubing  of 
different  diameters,  two  glasses,  lamp  wick,  block  of 
wood. 

Materials:     Cube  sugar,  red  ink. 

a.  Fill  one  of  the  glasses  with  water  and  place  the 
tubes  in  it.     Describe  how  the  water  goes  up  the  tubes. 
A  little  red  ink,  added  to  the  water,  will  make  it  easier 
to  see  the  water  in  the  tubes.       In  which  tube  does  the 
water  go  the  highest?     You  can  make  a  very  fine  glass 
tube  by  heating  a  short  piece  of  ordinary  glass  tubing   in 
the  flame  of  a  wing  burner,  and  then  suddenly  pulling  the 
two  ends  as  far  apart  as  you  can  reach.     Water  will  go 
six  or  eight  inches  up  such  a  tube.     Try  it. 

b.  Fill  one  glass  with  water  and  place  it  upon  the 
block  of  wood.       Now  wet  the  lamp    wick    thoroughly, 
wring  it  as  dry  as  possible    and 

bend  it  over  the  edge  of  the 
glass  so  that  it  reaches  the  bot- 
tom of  the  glass,  while  the 
other  end  falls  into  the  other 
glass  placed  near  the  block.  The 
lower  glass  should  be  empty. 
Tell  what  happens  in  a  few  min- 
utes. What  is  this  an  example  of?  The  oil  in  a  lamp 
reaches  the  flame  in  the  same  way. 

c.  Dip  one  corner  of  a  lump  of  sugar  in  some  colored 


108  WATER 

water  and  see  how  quickly  the  water  passes  through  the 
whole  lump. 


Capillarity  acts  in  all  directions.**  Thus  if  we  lay  .a 
lamp  wick  flat  upon  a  table  with  one  of  its  ends  in  a  little 
pool  of  water  the  other  end  will  soon  be  wet.  Capillar- 
ity acts  faster  downward  than  in  any  other  direction. 
Can  you  explain  why  this  is  so?  When  you  put  a  drop 
of  ink  upon  a  blotter,  how  does  it  act?  What  causes  it 
to  act  in  this  manner?  Think  of  all  the  examples  of 
capillarity  you  can.  Bodies  must  be  porous  in  order 
that  there  may  be  the  little  holes  in  which  capillarity  miv 
act.  If  we  wish  to  stop  capillarity  we  must  close  the 
holes. 

We  have  learned  that  water  is  necessary  for  plants 
and  that  the  soil  must  be  kept  damp  if  we  expect  the 
plants  to  grow  well.  How  do  you  suppose  that  the  soil 
holds  the  water?  Did  you  ever  see  water  put  into  a 
saucer  which  was  placed  under  a  flower  pot?  How  did 
the  plant  obtain  the  water?  All  soils  are  not  the  same 
in  their  ability  to  hold,  or  take  up,  water  and  the  follow- 
ing experiment  will  show  the  right  kind  of  soil  to  use  for 
flowers. 

Experiment  54. — How  Water  is  Held  in  the  Soil. 

Apparatus:  Chalk  box,  or  other  small  box,  with 
four  or  five  holes  in  one  side  large  enough  to  hold  stu- 
dent lamp  chimneys,  four  or  five  student  lamp  chimneys, 
with  cheese  cloth  tied  over  their  smaller  ends,  pan. 


CAPILLARITY   IN   SOILS 


109 


Materials:     Gravel,  sand,  coarse  soil,  fine  soil,  vege- 
table mold. 

a.  Arrange  the  apparatus  as  shown  in  the  illustra- 
tion and  have 
the  water  cover 
the  ends  of  the 
chimneys.  Fill 
each  chimney 
with  a  different 
kind  of  material. 
In  which  does!!! 
the  water  rise 
the  highest?  In 
which  does  the  water  rise  the  fastest?  Which  soil  would 
you  prefer  to  have  on  your  farm,  if  you  were  a  farmer? 


The  farmer  is  very  much  concerned  with  capillarity 
and  we  will  study  it  some  more  when  we  come  to  Section 
54,  in  which  we  shall  learn  that  the  farm  is  just  like  a 
workshop.  Capillarity,  besides  bringing  the  water  to  the 
roots  of  plants,  is  one  of  the  causes  of  the  rise  of  sap  in 
the  stalks  of  plants  and  trunks  of  trees.  The  evapo- 
ration of  water  from  the  leaves  aids  the  rise  of  sap,  just 
as  the  burning  of  the  oil  in  lamps  aids  the  capillarity  in 
the  wicks  in  bringing  the  oil  to  the  flame.  The  next 


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110  WATER 

experiment  will  prove  that  capillarity  acts  in  plants,  as 
well  as  showing  where  the  sap  rises. 

Experiment  55. — Capillarity  in  Plants. 
Apparatus :     Glass,  knife. 

Materials:  Red  ink,  twigs  of  any  tree  having  flat 
leaves. 

a.  Cut  a  few  twigs  and  put  them  immediately  into 
some  water  which  is  strongly  colored  with  red  ink.  Place 
the  glass  in  the  sun  and  in  a  draft  of  air,  if  possible.  At 
the  end  of  ten  minutes  remove  one  twig  and  split  it 
lengthwise.  Where  did  the  colored  water  go?  Remove 
another  twig  at  the  end  of  half  an  hour  and  examine  in 
the  same  way.  Leave  another  twig  for  a  full  day.  How 
do  the  leaves  appear?  How  did  the  colored  water  get 
through  the  stem?  Make  a  drawing  of  the  twig,  split 
lengthwise,  showing  just  where  the  colored  water  passed 
through  it. 


If  the  stalks  of  plants  are  not  woody,  they  receive 
their  stiffness  from  the  capillary  tubes  in  them  being  full 
of  water.  If  the  plants  do  not  receive  enough  water  the 
tubes  become  empty  and  the  stalks  flabby.  We  say.  that 
the  plants  wilt.  When  is  a  garden  hose  stiffer,  full  of 
water  or  empty? 

Review  Questions,  21. 

1.  What  was  the  position  of  the  Great  Dipper  last 
night  at  eight  o'clock? 

2.  What  are  the  uses  of  nitrogen? 


REVIEW  QUESTIONS  111 

3.  How  is  carbon  dioxide  harmful  and  in  what  way 
is  it  helpful? 

4.  What  are  some  of  the  oddities  of  solution? 

5.  Name  all  the  uses  of  water.     Which  one  is  the 
most  important? 

6.  Why  is  soft    water    cheaper    to    use    than    hard 
water  although  the  same  price  is  paid  for  each? 

7.  How  can  you  prove    that    plants    obtain    water 
from  below  the  surface  of  the  ground?     How  do  they  do 
it? 

8.  Why     is     wet    earth    heavier    than    dry    earth? 
Which  kind  of  earth  would  be  heavier  when  wet,  a  fine 
earth  or  a  coarse  earth?     Explain. 

9.  Why  do  farmers  break  up  the  soil  so  that    it  is 
fine,  before  they  plant? 

•  10.     Why  do  our  feet  become  wet  when  we  walk  on 
the  wet  sidewalk? 


THE  GUIDE 


PLANTS  AND  ANIMALS. 

42.     The  Beginning  of  Plant  Life. 

The  beginning  of  all  plant  life  is  in 'the  seed.  As 
long  as  the  seed  remains  dry  the  little  plant  rests,  but  as 
soon  as  water  is  absorbed  by  the  seed  it  cracks  open  and 
the  tiny  plant  begins  to  grow.  Let  us  examine  some 
seeds  and  learn  how  the  plant  gets  its  first  start. 

Experiment  56.— The  "Pocket  Garden." 
Apparatus:     A  plate  and  a  saucer. 
Materials:     Blotting    paper,    seeds    of    beet,    bean, 
corn,  pea,  radish,  squash. 

a.     Lay  a  square  of  blotting  paper  upon    the  plate 


and  upon  it  place  the  seeds.  Cover  the  seeds  with  an- 
other square  of  blotting  paper  and  moisten  both  with 
water.  Now  cover  all  with  the  saucer.  Keep  the  blotting 
paper  moist  but  do  not  have  the  seeds  under  water. 
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Elem.Sci.  8 


114  PLANTS  AND  ANIMALS 

Keep  in  a  warm  place  and  examine  once  a  day,  noting 
the  order  in  which  the  seeds  sprout. 

b.  Make  several  drawings  of  each    seed,    showing 
the  method  by  which  the   baby  plant   comes   out   of  the 
seed. 

c.  Write  a  description  of  the  roots,  stem,  and  leaves 
of  each  plant.* 

Note  to  teachers:  This  work  may  be  extended  over  con- 
siderable time  and  many  other  seeds  may  be  sprouted.  The 
drawing's  and  descriptions  would  make  a  good  supplement  to 
the  English  and  art  work. 

43.     The  Testing  of  Seeds. 

All  seeds  do  not  sprout  because  all  of  them  are  not 
perfect  seeds,  or  have  been  harmed  in  some  manner.  It 
is  of  very  great  importance  to  the  farmer  that  he  obtain 
good  seed,  for  otherwise  he  might  plant  many  seeds 
which  would  not  grow.  Thus  the  crop  would  be  less 
than  it  should  be  and  the  farm  would  not  be  as  productive 
as  it  might  otherwise  be.  Most  farmers  now  test  their 
seeds  because  they  have  learned  that  a  little  trouble  in  the 
beginning  will  save  them  much  money  in  the  end.  The 
testing  of  seeds  to  see  if  they  will  all  sprout  is  called  the 
germination  test. 

.    Experiment  57. — *  Germination  Tests. 

Apparatus:     Shallow  wooden  tray,  tacks,  string. 

Materials:  Sand,  seeds  of  various  kinds  from  va- 
rious stores. 

a.  Mark  off  the  sides  of  the  box  into  two-inch  spaces 
and  drive  a  tack  at  each  mark.  Now  lace  the  piece  of 
string  backward  and  forward  so  as  to  divide  the  open 
end  of  the  tray  into  squares,  two  inches  on  each  side. 

*  Adaoted  from  Farmers'  Bulletin  408,  U.  S.  Dept.  of  Agriculture. 


TESTING  SEEDS 


115 


. 


Mark  the  sides  of  the  tray  as  shown  in  the  illustration 
and  fill  the  box  with  dry  sand,  heaping  it  a  little.  After 
scraping  off  the  sand  with  a  straight  stick  the  tray  is 
ready  for  planting. 

b.  Plant  at  least  five  seeds  in  each  square  and  plant 
as  many  kinds  of  seeds  as  possible.       The  seeds  should 
just  be  covered  by  the  sand.       The  same  kind  of  seeds 
which  are  bought  at  different  stores,  or  obtained  from 
different  places  may  be  considered  as  different  seeds.    On 
a  page  in  your  note  book  mark  the  kinds  of  seed  and  the 
place  from  which  you  obtained  them,  together  with  the 
number  of  the  square  in  which  you  planted  them.    Count 
the  number  marked  at  the  left  end  of  any  row  as  tern  and 
add  to  this  the  unit  number  which  is  marked  at  the  right 
end  of  any  row.     Do  not  count  the  zero. 

c.  Water  the  sand,  after    planting    the    seeds,    by 
pouring  the  water  upon  a  piece  of  paper  placed  on  the 
sand.       Keeo  in  a  wirm  room,  watering  now  and  then. 
and  watch  for  the  little  plants.     In  about  a  week  all  of 

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115  PLANTS  AND  ANIMALS 

the  seeds  which  are  good  will  have  sprouted.     Good  seed 
should  have  every  seed  sprout. 


44.     The  Proper  Planting  of  Seeds. 

While  good  seeds  are  neces-sary,  if  they  are  not 
properly  planted  they  will  not  grow  well  and  perhaps 
not  at  all.  If  the  seeds  are  planted  too  deeply  they  may 
die  before  they  can  reach  the  light,  while  if  they  are  not 
planted  deeply  enough  they  may  become  dried  by  the 
sun  and  killed  by  too  much  light  upon  the  delicate  roots. 
The  depth  of  planting  of  seeds  varies  from  one-eighth  o£ 
an  inch,  in  the  case  of  celery  seeds,  to  four  inches  in  the 
case  of  the  white  potato.  If  the  ground  is  very  damp 
the  seeds  may  be  planted  less  deep  than  if  the  ground  is 
quite  dry.  Why?  Sometimes  seed  beds  are  shaded 
from  the  sun.  Can  you  explain  the  reason? 

There  was  no  way  for  man  to  discover  the  proper 
depth  of  planting  except  by  experimenting.  We  can  now 
use  the  knowledge  that  has  been  acquired  by  others  and 
tints  save  time.  However,  let  us  try  the  experiment  on  a 
few  different  seeds  in  order  to  see  why  it  is  that  the 
plants  do  not  grow  well  if  the  seeds  are  not  planted  at 
the  Drooer  depth. 

Experiment  58. — *The  Proper  Depth  of  Planting. 

Apparatus:  Several  deep,  wide-mouthed  bottles., 
such  as  pickle  bottles,  black  cloth  to  cover  bottles. 

Materials:  Loam,  seeds  of  various  vegetables  and 
flowers. 


THE  PROPER  DEPTH  OF  PLANTING. 


117 


a.  Sprinkle  about  an  inch  of  loam  in  the  bottom  of 
the  bottle  and  place  one  seed  of  each 
of  four  or  five  different  kinds  on 
the  surface  of  the  loam,  next  to  the 
glass  so  that  they  can  be  seen  when 
they  are  covered  with  loam.  Then 
sprinkle  about  an  inch  more  of  loam 
and  repeat  with  the  same  kinds  of 
seeds  as  were  used  on  the  first  layer. 
Repeat  the  process  until  the  bottle  is 
full.  Other  pupils  may  use  different 
seeds.  Water  the  loam  so  that  it  is 
moist  but  not  wet.  Cover  the  bot- 
tle, or  bottles,  with  black  cloth,  so  as 
to  shut  out  the  light  from  the  seeds, 
keep  in  a  warm  place,  and  examine 
once  a  day.  Do  not  let  the  sun  shine 
upon  the  bottles. 

b.  When  the  seeds  begin  to  sprout 
mike  drawings  of  the  way  in  which 
the  plant  comes  out  of  the  seed  and 
the  way  in  which  the  root  turns.  Make  drawings  of 
what  happens  to  those  seeds  which  were  planted  too 
deeply.  You  will  find  that  the  seeds  very  near  the  sur- 
face may  grow  all  right,  but  you  must  remember  that 
the  sun  did  not  shine  upon  the  loam.  Measure  the  depth 
which  you  find  is  proper  for  your  seeds,  and  obtain  from 
the  other  pupils  their  best  results. 


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118  PLANTS  AND  ANIMALS 

45.     The  Needs  of  the  Plant. 

We  have  learned  quite  a  lot  about  plants  and  now  we 
are  going  to  gather  the  information  together.  Science 
study  is  different  from  some  other  studies  because  in 
science  we  learn  a  number  of  facts  concerning  some- 
thing and  then  gather  all  these  facts  together  and  try  to 
learn  how  they  all  are  true  at  the  same  time.  Then  we 
can  form  an  idea  of  how  the  subject  studied  must  act  and 
how  it  would  act  if  conditions  were  different.  This  is 
called  drawing  conclusions.  Let  us  study  an  example : 
We  learned  in  Experiment  36  that  air  is  necessary  in 
order  that  plant  roots  may  grow.  Since  plants  start 
from  seeds  we  might  think  that  seeds  would  not  sprout 
if  they  were  not  supplied  with  air.  If  we  nearly  fill  a 
bottle  with  moist  earth  and  plant  a  few  beans  or  peas  in 
it,  and  then  stopple  it  tightly,  it  will  be  found  that  the 
seeds  will  not  grow.  Other  peas  and  beans  planted 
under  the  same  conditions  in  an  open  bottle  will  grow. 
Then  we  can  draw  our  conclusion  that  air  is  necessary 
for  plant  life  of  any  kind.  How  do  water  plants  get  air? 

We  are  always  told  to  keep  plants  in  a  warm  place 
so  that  they  may  grow  well.  Do  you  think  that  if  seeds 
are  not  kept  warm  they  will  grow?  Draw  your  conclu- 
sions from  the  last  paragraph— and  then  try  the  exper- 
iment. Place  some  seeds  in  moist  loa'm  and  put  it  in  the 
ice  chest,  or  try  the  experiment  during  cold  weather. 
Light,  which  is  so  closely  connected  with  heat,  is  also, 
necessary  for  green  plants,  as  we  learned  in  Section  11. 

In  the  germination  tests,  which  you  are  making,  you 
are  discovering  that  although  water  is  necessary  for 
plant  life,  the  plants  die  if  they  are  supplied  only  with 
water.  They,  like  animals,  require  food  and  they  obtain 


THE  NEEDS  OF  THE  PLANT  119 

their  food  from  the  ground.  If  the  ground  is  not  rich 
the  plants  will  not  grow  well  because  they  will  not  be 
able  to  obtain  enough  food.  Farmers  add  plant-food  to 
the  ground,  where  the  ground  is  not  rich  enough.  Any 
plant-food  which  is  added  to  the  ground  is  called  a  fertil- 
izer. All  plant-food  must  be  such  as  will  dissolve 
in  water  after  it  is  put  upon  the  ground. 

Thus  plants  need  light,  heat,  air,  water,  and  food.   Do 
you  think  that  you  need  much  more  in  order  to  live? 

Review  Questions,  22. 

1.  Why  do  plants  grow  best  in  summer?     Give  sev- 
eral reasons.       Why  is  the  glass  of  greenhouses  some- 
times covered  with  white  paint? 

2.  Why  is  it  bad  for  a  plant  to  soak  the  soil    with 
water  so  that  the  water  stands  on  the  surface  of  the  soil 
for  several  hours? 

3.  Why  does  water  go  into  the  soil? 

4.  If  you  were  buying  a  farm  how  would  you  decide 
whether  the  soil  was  good? 

5.  Why  do  the  plants  soon  die  in   Experiment  5fi? 
Which  plants  live  the  longer,  those  from  large  seeds  or 
from  small  seeds? 

6.  What  is  the  advantage  of  germination  tests? 

7.  Why  is  the  sand  watered  in  Experiment  57  by 
pouring  the  water  upon  a  piece  of  paper? 

8.  Why  is  it  necessary  to  know  the  proper  depth  of 
planting?     Do  you  think  that  a  difference  of  a  quarter  of 
an  inch  would  do  any  harm  to  a  seed  which  should  be 
planted  two  inches  deep? 

9.  Name  and  discuss  all  the  needs  of  a  plant. 


120 


PLANTS  AND  ANIMALS 


10.  Name  all  your  needs  besides  the  needs  of  the 
plant  and  see  if  they  really  are  necessary. 

46.     *Birds. 

In  the  minds  of  farmers  birds  are  closely  connected 
with  seeds.  The  birds  visit  the  fields  as  soon  as  they  are 
planted  and  the  farmer  views  them  with  suspicion.  The 
birds,  as  a  rule,  eat  very  few  seeds  of  farm  crops,  and 
they  are  much  more  interested  in  getting"  the  worms  and 
insects  which  have  been  exposed  by  the  cultivaticn  of 
the  land.  Since  many  of  the  insects  which  the  birds  eat 


Cut  supplied  through  United  States  Department  of  Agriculture. 
*     See  Appendix. 


BIRDS 


121 


are  those  which  harm  the  crops,  the  birds  are  really  the 
farmers'  friends.  Nearly  one-tenth  of  the  crops  are 
destroyed  by  insects,  even  with  the  birds  eating  all  the 
insects  they  can.  If  the  birds  were  destroyed  it  would  be 
doubtful  if  a  satisfactory  crop  could  be  raised.  The  birds 
do  eat  seeds,  but  they  are  very  fond  of  weed  seeds  so  that 
they  help  the  farmer  also  in  this  case.  Weeds  can  grow 
better  than  the  crops,  and  they  take  the  water  from  the 
soil  which  the  crops  need. 

Not  only  do  the  birds  help  the  farmer  but  they  also 
protect  the  forests  to  a  great  extent.  Many  of  the  forest 
trees  are  easily  attacked  by  boring  beetles  and  ants.  The 
harm  which  is  due  to  these  wood-boring  insects  is 
increased  by  decay  which  begins  to  take  place  around  the 
holes.  In  Section  48  we  will  learn  more  about  the  decay 
of  trees.  The  large  illustration  is  the  familiar  wood- 
pecker, called  the  flicker.  Like  other  wookpeckers  it  is 
one  of  the  chief 
preservers  of  the 
forests  and 
should  be  pro- 
tected in  every 
way.  The  small 
illustration  is  the 
well  -known 
phoebe  whose 
chief  food  is 
harmful  insects, 
the  rest  of  the 
food  being  wild 
fruit. 


Cut    supplied  through   United    States  Department  of  Agriculture. 


122  PLANTS  AXD  AXIMALS 

47.     "Wild  and  Garden  Flowers. 

The  names  of  the  common  garden  and  wild  flowers 
should  be  learned  and  associated  with  them.  The  only 
way  to  do  this  is  to  bring  a  few  flowers  to  school  and 
compare  them  with  the  illustrations  in  the  large  refer- 
ence book  which  tells  all  about  them.  Gradually  you 
will  learn  the  names  of  all  the  common  flowers  as  well  as 
some  of  the  rarer  ones.  The  best  way  to  learn  so  that 
you  will  remember  is  to  make  a  collection  of  the  flowers 
and  write  a  brief  description  on  the  paper  upon  which 
you  mount  each  flower.  Then  you  can  always  review 
your  own  work  and  often  learn  more  than  you  would 
from  just  reading  a  book.  The  next  experiment  should 
be  continued  until  there  are  no  flowers  of  the  neighbor- 
hood which  you  do  not  have  in  your  collection.  See 
which  pupil  can  make  the  best  collection,  but  remember 
that  "The  race  is  not  always  to  the  swift." 

Experiment  59. — A  Flower  Collection. 

Materials:  Sheets  of  soft,  unglazed  paper  cut 
17"xll",  folded  so  that  they  are  Il"x8^",  strips  of 
gummed  paper  y\"  wide. 

a.  Take  one  of  your  flowers,  which  should  have  a 
long  stem  but  not  longer  than  ten  inches,  and  several 
leaves,  and  compare  it  with  the  reference  book.  After 
you  have  learned  its  name  and  habits  arrange  it  in  the 
prettiest  manner  possible,  on  the  right  side  of  the  fold, 
having  the  paper  unfolded.  Try  to  remember  how  the 
plant  was  growing  and  arrange  it  as  it  was,  because  the 
natural  way  is  always  the  prettiest.  Cut  the  gummed 
paper  into  lengths  so  that  they  will  pass  over  the  stems 

*     See   Appendix. 


TREES  123 

and  have  a  good  hold  upon  the  paper  on  each  side  of 
the  stems,  when  pasted  down.  Do  not  use  the  strips  too 
long  nor  too  plentifully.  The  flowers  and  leaves  should 
be  fastened  so  that  they  cannot  move,  but  too  many  strips 
do  not  look  well.  After  a  plant  is  nicely  fastened,  cover 
;t  with  the  left  hand  part  of  the  paper  and  press  under 
several  large  books  until  dry.  Then  write  its  name  and 
description  in  the  place  on  the  right  hand  page  where 
there  is  the  most  room. 

48.     *Trees. 

The  value  of  trees  to  man  is  very  great.  We  have 
learned  that  trees  take  in  carbon  dioxide  and  give  out 
oxygen.  This  is  of  more  importance  in  our  cities  than 
in  the  open  country  for  there  are  many  fires  in  houses 
and  factories,  all  of  which  are  producing  vast  quantities 
of  carbon  dioxide.  Although  the  wind  blows  part  of 
this  away  and  the  rain  washes  some  of  it  into  the  ground, 
yet  it  is  most  important  that  we  have  as  many  trees  as 
possible  in  our  cities.  Trees,  as  well  as  all  other  plants, 
give  off  a  huge  amount  of  water  by  transpiration  and 
change  the  climate  of  a  locality  very  much.  See  Sec- 
tion 40.  Trees  also  reduce  the  violence  of  winds.  Final- 
ly, trees  are  beautiful. 

While  trees,  are  of  very  great  value  in  cities  they  are 
of  still  greater  value  to  the  nation  in  whose  forests  they 
grow.  When  rain  falls  upon  bare  ground  most  of  it  runs 
off,  wearing  the  soil  away  and  doing  no  good.  After  the 
rain  is  over  there  is  very  little  water  left  in  the  soil,  and 
this  soon  dries  up  in  the  bright  sunlight.  If  the  ground 
is  dry  there  will  be  no  streams  or  rivers  soon  after  the 

*     See   Appendix. 


124  PLANTS  ANT)  ANIMALS 

rain  has  ceased  to  fall,  although  the  water  which  ran  off 
the  bare  ground  during  the  rain  may  have  caused  floods. 
If  there  are  forests,  however,  the  leaves  gather  much  of 
the  rain  and  cause  it  to  drip  slowly  to  the  ground.  There 
it  is  caught  in  the  mass  of  dead  leaves  and  twigs  and 
cannot  run  away.  Thus  it  slowly  sinks  into  the  ground- 
until  the  soil  is  wet  many  feet  deep.  When  the  rain 
ceases  the  sun  cannot  cause  the  water  to  evaporate 
bemuse  the  thick  shade  of  the  forest  keeps  it  out.  The 
water  slowly  passes  away  by  capillarity  and  thus  the 
streams  and  rivers  flow  for  a  long  time. 

The  government  of  the  United  States  has  set  aside 
vast  forests  called  National  Forests  in  order  to  regulate 
the  flow  of  water,  as  well  as  to  keep  up  a  supply  of 
wood.  The  older  trees  are  cut  and  younger  ones  are 
allowed  to  grow  in  their  places.  The  chief  enemies  of 
the  forest  are  fire  and  insects.  Men,  called  Forest 
Rangers,  protect  the  trees  against  fire,  and  our  friends 
the  woodpeckers,  eat  the  insects.  The  illustration  shows 
how  "frogstools"  indicate  that  decay  has  begun.  The 
frogstools  live  upon  the  trees  where  insects  have  made 
holes  in  the  bark.  Just  as  our  skin  protects  us  from 
bacteria  so  the  bark  protects  trees  from  decay.  The 
heirt  of  a  tree  may  be  decayed  and  the  tree  will  still  live, 
for  its  r-rowth  is  on  the  outside.  In  what  part  of  the 
twigs  did  the  red  ink  rise  in  Experiment  55?  Each  year 
a  ring  is  added  around  the  trunk  of  a  tree,  unless  decay 
is  taking  place  on  the  outside  of  it,  and  by  counting  the 
rings  on  the  stump  of  a  tree  which  has  been  cut  down  you 
can  tell  its  age. 

Just  as  with  flowers,  we  should  know  the  common 
trees  by  name.  It  is  not  possible  to  make  a  collection 


TREES  125 

of  trees  but  we  can  collect  the  leaves  and  seeds  and  per- 
haps get  pieces  of  the  bark  and  wood. 


Experiment  60.— A  "Tree"  Collection. 

a.  Collect  the  leaves  of  all  the  different  trees  you 
can  find  in  the  neighborhood  and  mount  them  in  the  same 
way  as  you  mounted  the  flowers  in  the  last  experiment. 

Cut    supplied   through    United    States  Department  of  Agriculture. 


126  PLANTS  AND  ANIMALS' 

Look  up  their  names  and  habits  in  the  reference  book  and 
write  a  brief  description  of  each  kind  upon  the  paper 
upon  which  you  have  mounted  the  leaves. 

b.  Try  to  obtain  pieces  of  trees  with  the  bark  on. 
Saw  these  lengthwise,  and  polish  them  with  sandpaper, 
after  they  are  thoroughly  dry.     Label    them    carefully. 
To  keep  the  collection,  a  screw  eye  may  be  inserted  in 
one  end  and  the  samples  hung  on  hooks  which    are  the 
right  distance  apart. 

c.  A  collection  should  also  be  made  of  the  seeds  and 
seed  cases  of  all  the  trees.       These    may    be    placed    in 
small  cardboard  boxes  which  are  properly  labeled. 


It  would  be  a  good  plan  for  you  to  write  some  letters 
to  pupils  in  other  cities  and  states,  telling  them  what  you 
are  doing  and  asking  them  to  send  you  samples  of  flow- 
ers, leaves,  wood,  and  seeds  which  grow  there  and  which 
do  not  grow  near  your  school.  In  return  you  would 
send  samples  which  they  did  not  have.  Of  course  you 
would  send  your  best  work. 

The  seeds  of  trees  grow  in  an  interesting  manner  as 
you  will  see  by  the  next  experiment. 

Experiment  61. — Planting  Tree  Seeds. 

Apparatus:     Box  filled  with  sand. 

Materials:  Acorns  and  other  soft-shelled  nuts, 
seeds  of  the  apple,  pear,  orange  and  lemon  trees,  and  any 
other  tree  seeds  which  are  easily  obtainable. 

a.  Plant  the  seeds  or  nuts  about  one  inch  deep  in 
the  sand'  and  keep  it  moist.  When  the  seedlings  have 


REVIEW  QUESTIONS  127 

come  up  they  may  be  transplanted  into  tin  cans  filled 
with  good  soil,  and  allowed  to  grow.  There  should  be 
openings  in  the  bottom  of  the  cans?  Why?  Make  a 
drawing  of  how  each  kind  of  tree  starts  from  its  seed. 

b.  When  the  little  trees  are  a  few  inches  high  they 
may  be  taken  home  and  placed  in  the  garden,  unless  they 
are  trees  which  cannot  live  in  your  climate.  In  this  case 
they  must  be  kept  in  the  house. 

Review  Questions,  23. 

1.  How  can  you  show  that  plants  need  light? 

2.  What  is  a  flame  ?       How  can    you    prove    your 
answer? 

3.  Do  all  crystals  have  the  same  shape? 

4.  Name  six  of  the  harmful  drinks.  Do  they  always 
show  the  harm  which  they  are  doing? 

5.  What  causes  water  to  be  hard? 

6.  How  do  birds  help  the  farmer?       How  do  they 
harm  him?     Which  is  greater,  the  help  or  the  harm? 

7.  What  is  the  good    of    knowing    the    names    of 
flowers? 

8.  Parks  have  been  called  the  "breathing  places"  of 
a  city.     Explain  why  this  is  a  good  name. 

9.  If  all  the  forests  were  burned  or  chopped  down 
what  would  be  the  effect  upon  the  'country? 

10.  Name  all  the  advantages  of  having  forests. 

49.     A  Queer  Plant— Yeast. 

All  the  plants  which  we  have  studied,  except  bac- 
teria, have  been  large  enough  to  be  seen.  All  of  these 
visible  plants  have  needed  light,  heat,  air,  water  and 


128  PLANTS  AND   ANIMALS 

food  in  order  to  live.  They  have  taken  in  carbon  diox- 
ide and  given  out  oxygen.  They  have  had  leaves,  flow- 
ers, stalks  and  roots,  and  have  grown  from  seeds.  Now 
we  are  going  to  study  a  very  queer  plant  which  has  no 
roots,  stalk,  leaves,  flowers  nor  seeds.  This  plant  is 
called  yeast  and  all  its  needs  are  sugar  and  water  and  a 
little  heat. 

Yeast  plants  are  so  small  that  they  cannot  be  seen 
by  the  use  of  the  simple  microscope,  but  it  is  necessary 
to  use  a  very  powerful  microscope.  An  ordinary  yeast 
cake  contains  millions  of  these 
little  plants.  If  sugar,  water,  and 
a  little  heat  are  supplied,  each 
tiny  plant  begins  to  send  out  a 
Httle  swelling  called  a  projection 
which  increases  in  size  until  it  is 
nearly  as  large,  as  the  plant  itself. 
Then  it  breaks  off  and  becomes  a 
separate  plant.  Such  growth  is 
called  budding.  The  illustration 
shows  the  process  of  budding  in 
nine  stages. 

When  the  yeast  plants  are  growing  they  change  the 
sugar  into  carbon  dioxide  and  alcohol.  The  process  of 
changing  sugar  in  this  manner  is  called  fermentation. 
Most  yeast  cannot  grow  without  sugar.  The  following 
experiment  will  prove  that  carbon  dioxide  is  produced 
when  yeast  grows,  while  Section  79  will  discuss  the 
manufacture  of  alcohol. 

Experiment  62. — Fermentation. 
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YEAST   AND   BACTERIA  129 

Apparatus:  The  apparatus  may  be  as  shown  in  the 
illustration  on  page  104,  or  a  pickle  bottle  may  be  used  in 
the  place  of  the  flask.  A  box  may  be  used  in  the  place 
of  the  ring-  stand. 

Materials:     Yeast  cake,  molasses. 

a.  Dissolve  the  yeast  cake  in  a  small  amount  of 
water  and  put  it  into  the  bottle  which  should  be  filled  not 
more  than  one-third  full  of  lukewarm  water.  Add  two 
tablespoonfuls  of  molasses  and  shake  well.  Insert  the 
stopple  and  place  the  tube  in  test  tube  which  should  be 
half  full  of  limewater.  In  a  few  minutes  bubbles  will 
begin  to  come  from  the  molasses  and  pass  into  the  lime- 
water.  How  do  you  know  that  the  gas  is  carbon  diox- 
ide? Compare  this  experiment  with  Experiment  41. 

While  the  first  illustra- 
tion of  yeast  shows  the 
growth  of  a  single  yeast 
plant,  it  must  be  remem- 
bered that  in  a  mass  of 
yeast  the  plants  will  be 
found  in  all  stages  of 
growth.  The  illustration^ 
shows  what  would  be 
seen  if  a  small  mass  of 
yeast  were  examined  un- 
der a  very  strong  micro- 
scope. See  Section  78. 

50.      Another  Queer  Kind  of  Plant — The  Bacteria. 

In  several  of  our  lessons  we  have  read  a  little  about 
the  plants  called  bacteria  and  have  learned  that  they 
grow  fast  in  warm,  damp  places  where  the  sun  does  not 

Cut    supplied   through    United    States  Department  of  Agriculture. 

Elem.  Sci.  9 


Orf© 

Vii^X 


130  PLANTS  AND  ANIMALS 

reach.  We  also  learned  that  they  may  cause  disease  but 
that  they  can  be  killed  by  heat,  bright  sunshine  and  by 
antiseptic  washes. 

The  bacteria  are  much  smaller  than  the  yeasts  and 
can  only  be  seen  by  the  use  of  a  very  powerful  micro- 
scope. They  need  moisture  and  a  little  warmth  in  order 
to  grow,  but  they  can  live  on  almost  any  kind  of  food. 
Each  increases  in  numbers  very  rapidly,  if  supplied  with 
food,  in  a  manner  somewhat  similar  to  yeasts.  Instead 
of  budding,  however,  each  becomes  longer  and  separates 
in  the  middle  into  two  bacteria.  This  method  of  increase 
is  called  fission.  Under  favorable  conditions  a  single 
bacterium  will  produce  seventeen  million  bacteria  in 
twelve  hours. 

Bacteria  are  the  cause  of  many  of  the  more  delicate 
flavors  of  food.  Thus  butter  and  most  kinds  of  cheese 
owe  their  peculiar  flavor  to  the  growth  of  bacteria.  It 
is  due  to  bacteria  that  the  nitrogen  of  the  air  can  be 
changed  into  food  which  is  suitable  for  plants.  See 
Section  31.  There  are  also  several  beneficial  changes  irr 
substances  for  which  we  must  thank  the  bacteria.  It  im- 
probable that  there  could  be  no  life  if  it  were  not  for  the 
effects  which  are  produced  by  bacteria.  Thus  we  see 
that  they  are  our  friends. 

Some  kinds  of  bacteria  are  very  harmful,  and  we 
should  learn  how  to  protect  ourselves  from  them.  Be- 
fore studying  how  to  preserve  our  health  let  us  learn 
what  the  bacteria- do  to  materials  upon  which  they  feed. 

51.     Souring  and  Decay. 

When  bacteria  have  been  present  in  food  for  some 
time,  they  change  it  into  substances  which  have  bad 
odors  and  flavors..  The  food  is  spoiled  and  we  call  this 


SOURING  AND  DECAY  131 

spoiling  decay.  If  the  bacteria  had  not  been  present 
there  would  have  been  no  change  at  all  .in  the  food.  So 
the  bacteria  spoil  our  food  and  thus  are  our  enemies.  If 
the  only  effect  which  the  bacteria  have  upon  food  were 
merely  to  spoil  it  we  would  not  have  to  take  so  much 
care  of  it.  In  addition  to  spoiling  the  flavor  of  our  food 
and  causing  it  to  have  a  bad  odor,  the  bacteria  produce 
certain  poisons,  called  ptomaines.  The  ptomaines  may 
be  formed  to  a  degree  sufficient  to  poison  us  without 
there  being  any  disagreeable  odor  or  flavor  to  the  food. 
These  poisons  are  very  dangerous  and  we  should  be 
careful  not  to  eat  old  food,  or  food  which  has  remained 
long  in  a  warm  place.  Cooking  the  food  does  not  destroy 
the  ptomaines. 

Another  kind  of  bacteria  changes  cider  and  grape 
juice  into  vinegar.  The  mass  of  slimy  material  which  is 
always  found  in  vinegar,  called  mother  of  vinegar,  is  com- 
posed entirely  of  countless  millions  of  bacteria.  Vine- 
gar is  one  of  the  class  of  materials  which  are  called  acids. 
You  can  always  detect  an  acid  by  its  sour  taste.  When 
milk  sours  it  is  because  an  acid  has  been  produced  in  it 
by  bacteria.  In  the  following  experiment  on  milk  we 
can  learn  what  is  necessary  to  preserve  food  of  all  kinds. 

Experiment  63. — How  to  Preserve  Milk. 

Apparatus:  Can  or  dish  in  which  to  boil  water, 
ring  stand,  burner,  4  test  tubes  or  small  bottles. 

Materials:     Milk,  borax,  cotton,  labels,  boiling  soda. 

a.  Label  the  test  tubes  No.  1,  2,  3,  4  and  fill  them 
one-half  full  of  fresh  milk.  Set  one  aside,  just  as  it  is, 
in  a  warm  place,  put  the  second  one  in  as  cold  a  place  as 
possible.  To  the  third  add  a  pinch  of  borax  and  set  in 


132 


PLANTS  AND  ANIMALS 


a  warm  place.  The  fourth 
tube  should  have  a  plug 
of  cotton  put  into  the  top 
and  then  it  should  be 
placed  in  the  can  of  cold 
water  which  should 
gradually  be  heated  to 
176°F.  and  kept  at  about 
that  temperature  for  at 
least  five  minutes.  This 
heating  is  called  pasteur- 
ization. Then  set  it  in 
a  warm  place.  Examine  the  milk  once  a  day.  Which 
tube  sours  first?  Which  keeps  sweet  the  longest? 

b.     Add  a  little  boiling  soda    to  some    of  the    sour 
milk.       Notice  the  bubbles.     They    are  carbon    dioxide 
How  does  the  milk  taste? 

The  illustrationshows  the  kind  of  bacteria  which  caused 
the  milk  to  sour.  They  are  very  much  magnified. 

Bacteria  can  be  killed  by  heat  and  by  poisons.  The 
poisons  are  called  preservatives,  and  they  should  never 
be  used.  The  experiment  was  to  show  that  poisons  may 
preserve  food  but  they  are  harmful  and  unnecessary. 
The  growth  of  bacteria  may  be  made  very  slow  by  keep- 
ing the  food  cold.  Since  bacteria  require  moisture  in 
order  to  live,  if  the  food  is  dried  it  may  be  protected  from 
them.  Smoking  of  meat  and  fish,  as  well  as  drying,  will 
preserve  them  for  a  long  time.  Food  may  be  kept  moist 
and  yet  free  from  bacteria  by  the  use  of  salt,  sugar,  or 
spices  and  vinegar. 

After  the  bacteria,  which  are  in  or  on  the  food,  are 
killed  bv  heat  it  is  necessary  to  exclude  others.  This  is 


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DISEASE  AND  SANITATION 


133 


the  reason  for  sealing  preserves  and  canned  goods.  Why 
did  you  put  the  plug  of  cotton  in  the  test  tube  of  milk 
which  you  pasteurized? 

If  we  leave  food  upon  our  teeth  the  bacteria,  which 
are  always  present,  live  upon  this  food  and  produce  acids 
which  hurt  the  covering  of  our  teeth,  called  enamel.  If 
this  action  continues  very  long  the  enamel  is  destroyed 
and  then  the  bacteria  of  decay  cause  our  teeth  to  decay. 
For  this  reason  we  should  wash  our  teeth  at  least  twice 
a  day  and  always  before  going  to  bed.  When  the  enamel 
is  destroyed  the  repairs  which  a  dentist  may  make  are 
not  lasting  because  the  decay  goes  on  around  the  filling 
which  he  puts  into  the  tooth.  Thus  the  hole  or  cavity 
becomes  larger  and  larger  until  the  tooth  is  destroyed. 
52.  Disease  and  Sanitation. 

Some  bacteria  enter  the  body  and,  living  upon  the 
tissues,  produce  various  diseases.  All  bacteria  which 
enter  the  body  are  not  harmful  and  some  are  helofiil. 
Diseases  which  are  given  by  one  person  to  another  by 
means  of  bacteria  are  called  contagious.  Flies  are  car- 
riers of  disease  and  the  common  house  fly,  which  is 
shown  magnified  five  times,  is  one  of  our  worst  enemies. 

The  life  history  of  the  common  house    fly    is    very 


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134 


PLANTS  AND  ANIMALS 


rapid.  A  single  fly  lays 
about  one  hundred  and 
twenty  eggs  on  the  aver- 
age, in  manure  and  decay- 
ing material,  which  hatch 
within  a  day,  producing 
maggots  or  larvae.  The 
larvae  or  maggots  go  into 
the  pupal  or  quiet  stage 
after  a  few  days,  from 
which  stage  they  come 
forth  as  flies  in  less  than  a 
week.  The  puparium  is  shown  to  the  left  of  the  illustra- 
tion and  the  larva  to  the  right.  The  other  illustration 
shows  a  blue-bottle  fly, .also  magnified  five  times.  This  fly 
is  also  called  the  meat  fly,  and  breeds  in  decaying  animal 
matter.  All  of  these  flies  may  carry  disease.  The  com- 
mon house  fly  should  be  called  the  typhoid  fly  as  it  is  a 
carrier  of  that  disease. 

We  should  protect  ourselves  from  the  flies  by 
screens,  and  do  what  we  can  to  deprive  them  of  foods. 
No  decaying  materials  should  be  allowed  anywhere  in 
the  yard  or  neighborhood.  Horse  stables  should  have  a 
proper  place  for  storing  the  horse  manure  until  it  can  be 
carried  away.  Absolute  cleanliness  is  a  great  preven- 
tive of  flies.  Sticky  fly  paper  and  fly  traps  will  help  to 
remove  the  flies  which  come  into  the  house. 

The  diseases  which  are  caused  by  bacteria  are  dif- 
ferent from  the  poisons  which  the  bacteria  produce.  The 
ptomaines  act  quickly  while  the  diseases  take  several 
days,  or  perhaps  weeks,  in  which  to  develop.  The  devel- 

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REVIEW  QUESTIONS  135 

opment  of  a  disease  which  is  caused  by  bacteria  is  due 
to  their  growth  within  the  body.  If  the  body  is  in  a 
good  condition  the  bacteria  will  be  overcome  by  forces 
within  the  body ;  it  is  usually  a  weak  body  which  is  easily 
attacked  by  bacteria.  Thus  the  best  way  to  prevent 
being-  sick  is  to  take  good  care  of  the  body.  This  means 
eating  the  proper  food,  sleeping  enough  and  not  doing 
anything  which  is  harmful  to  the  body.  It  means  bodily 
cleanliness  and  clean  houses.  It  means  good  ventilation, 
plenty  of  sunlight,  and  breathing  fresh  air  both  day  and 
night. 

Cleanliness,  if  complete,  is  the  greatest  help  to  sani- 
tation.    Sanitation  means  freedom  from  harmful  bacteria. 
Review  Questions,  24. 

1.  What  use  is  made  of  nitrogen? 

2.  Name  all  the  sources  of  carbon  dioxide  we  have 
studied. 

3.  What  is  the  use  of  carbon  dioxide? 

4.  What  are  the  needs  of  all  living  things? 

5.  What  is  yeast?     What  can  yeast  do? 

6.  What  are  bacteria?     Are  all  bacteria  harmful? 

7.  How  can  you  keep  milk  from  souring?     Which 
is  the  worst  way  and  which  is  the  best  way? 

8.  Why  should  we  clean  our  teeth  at  night  when  no 
one  is  to  see  them? 

9.  Why  should  we  keep  clean? 

10.  What  is  the  best  way  to  prevent  being  sick? 

Next  year  we  shall  study  more  about  plants  and 
animals. Now  we  are  going  to  learn  about  what  plants 
and  animals  need  for  food  and  about  the  food  which 
thev  make. 


THE  GUIDE 


FOOD. 


53.     The  Source  of  All  Food. 

The  source  of  all  of  our  food  is  the  soil.  Plants 
grow  in  the  soil  and,  while  they  take  in  carbon  dioxide 
through  their  leaves  and  nitrogen,  after  it  has  been 
changed  by  the  bacteria,  through  their  roots,  they  could 
not  live  if  it  were  not  for  other  material  which  is  con- 
tained in  the  soil.  This  material  is  chiefly  potash  and 
phosphorus.  Animals  eat  the  plants  and  are  used  as  part 
of  the  food  of  man. 

Plant  food  and  animal  food  are  not  very  different 
in  regard  to  the  kinds  of  material  which  they  contain. 
The  difference  comes  in  the  proportions  in  which  they 
occur.  We  need  our  food  for  three  reasons :  to  give  us 
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. 

•0007&/V- 3.3% 

4.0% 


V4LU£  Pffi  POU/V0 


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138 


FOOD 


AS 


strength,  to  keep  us  warm,  and  to  store  up  fat.  The 
material  which  builds  up  the  muscles  and  aids  in  the 
growth  of  new  tissue  is  called  protein.  Lean  meat  and 
eggs  are  examples  of  food  which  contain  a  large  amount 
of  protein.  Peas  and  beans  are  the  vegetables  which 
contain  the  most  protein.  The  materials  which 
are  used  chiefly  for  producing  our  animal  heat 
are  called  carbohydrates.  Grains,  potatoes  and  other 
starchy  foods,  and  all  sugars  are  composed  largely  of 
carbohydrates.  Some  of  the  carbohydrates  are  trans- 
formed into  fat.  The  fats,  both  animal  and  vegetable 
are  used  to  produce  fat  in  the  body  but  they  also  produce 
a  large  amount  of  heat.  Animal  fats  are  butter,  lard  and 
the  other  fats  which  form  a  part  of  the  meat  which  we 
eat.  The  amount  of  heat  is  measured  by  the  calorie.  A 
calorie  will  raise  the  temperature  of  one  liter  of  water 
one  degree  Centigrade.  A  liter  is  the  measure  of  liquids 
in  the  French  system  and  is  a  little  more  than  a  quart 
See  Section  58. 


TYPE  Of-  ST/ILH'  YfGSTXBLf. 


7Z2V— 
T- 0.2 

G4/?SO- 


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THE  SOURCE  OF  ALL   FOOD 


139 


AS 


Milk  is  very  nearly  a  perfect  food.  The  illustration 
shows  a  glass  of  milk  and  the  divisions  indicate  the  dif- 
ferent parts  of  the  milk.  Such  a  drawing  is  called  a 
diagram.  The  other  illustrations  show  some  common 
vegetables.  Note  that  there  is  more  water  in  all  of  these 
vegetables  than  in  milk  This  is  true  of  nearly  all  vege- 
tables and  fruits,  before  they  are  dried.  Notice  also  that 
vegetables  have  very  little  fat.  For  this  reason  they  are 
good  for  summer  food,  as  we  need,  and  should  eat  very 
little  fat  in  warm  weather. 

In  Section  31  we  learned  that  ihe  bacteria  took  in 
the  nitrogen  from  the  air  and  changed  it  into  food  for 
plants,  and  that  it  was  this  food  which  if  we  ate  it, 


LETTUCE 


,45 


CAVL/FLOWE& 


-----  -94.7  '<#> 

0.3 

G4RBO- 


0.3 


ASH 


would  give  us  strength.  Protein  is  the  food  which  the 
plants  make  by  the  aid  of  the  bacteria.  So  again  we  see 
that  life  would  be  impossible  without  our  friendly  bac- 
teria. 


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140  FOOD 

54.     The  Farm  a  Workshop. 

For  a  long  time  people  thought  of  the  farm  as  a  place 
where  they  could  obtain  something  for  almost  nothing. 
All  that  they  had  to  do  was  to  plant  seeds  and  reap  the 
harvest.  When  it  became  necessary,  however,  to  raise  as 
large  crops  as  possible,  on  account  of  the  increased  num- 
ber of  persons  who  had  to  be  fed,  people  found  that  they 
must  consider  the  farm  as  a  workshop.  Just  as  the  ma- 
terials are  manufactured  into  the  finished  product  in  a 
workshop,  so  on  the  farm  the  food  for  the  plants  is  made 
into  vegetables  and  fruits. 

In  a  workshop  the  supply  of  material,  which  is  to  be 
used  to  manufacture  articles,  must  be  kept  in  large  quan- 
tities and  the  factories  cannot  produce  the  articles  unless 
they  have  a  proper  supply  of  material.  In  the  same  way 
every  plant  that  grows  and  every  fruit  or  vegetable  which 
is  produced  require  a  certain  amount  of  plant-food.  This 
plant-food  is  taken  from  the  ground  never  to  return. 
When  all  the  plant-food  has  been  removed  by  the  grow- 
ing plants,  no  more  plants  will  grow  in  that  soil.  We 
say  then  that  the  ground  is  sterile.  If  we  wish  to 
change  sterile  land  so  that  crops  may  be  raised  upon  it, 
we  must  put  into  the  soil  the  materials  which  plants 
require  to  make  them  live  and  grow.  Such  material  is 
called  a  fertilizer. 

A  good  farmer  never  allows  his  land  to  become 
sterile,  but  each  year  he  adds  to  the  ground  the  right  kind 
of  plant-food  for  the  crop  he  wishes  to  raise.  Now  you 
see  why  a  farm  should  be  considered  as  a  workshop — if 
you  want  a  good  crop  you  must  either  have  in  the  soil 
those  materials  which  the  plants  need  or  else  you  must 


THE  FARM  A  WORKSHOP  141 

put  them  there.  New  land  usually  has  a  good  supply  of 
plant-food.  Land  which  has  been  used  for  many  years 
must  have  fertilizers  added  to  it,  if  it  is  to  produce  good 
crops.  Plant-food  is  chiefly  phosphorus,  potash,  and 
nitrogen,  although  there  are  many  other  materials  which 
are  needed  in  small  quantities. 

All  other  kinds  of  business  depend  upon  the  farmers 
to  whom  we  must  look  for  our  food  of  all  kinds  except 
fish.  The  farmer  has  opportunities  in  his  business  which 
are  far  greater  than  those  found  in  other  lines  of  work. 
He  can,  by  experimenting,  produce  new  fruits  and  vege- 
tables, as  well  as  improve  those  which  we  already  have. 
He  is  a  producer,  that  is,  he  gives  to  the  world  something 
which  the  world  did  not  have  before.  Most  of  the  other 
kinds  of  business  take  what  has  been  produced  from  the 
earth  and  only  make  from  it  something  which  is  of  use. 
While  all  kinds  of  business  tend  to  make  the  world  a 
pleasanter  place  in  which  to  live,  the  farmer  is  the  only 
business  man  who  actually  makes  the  world  richer  for 
his  labor. 

55.     Tilling  the  Soil. 

When  we  consider  the  farm  a  workshop  in  which 
plant-food  is  changed  into  plants,  and  fruits,  and  vege- 
tables, we  must  remember  that  plants  require  a  large 
amount  of  water,  and  take  care  that  they  receive  it.  We 
learned  in  Section  48  that  if  rain  fell  upon  bare  ground 
it  all  would  run  off  rapidly  and  wear  the  soil  away. 
Where  the  land  is  level  the  run-off  is  not  nearly  as  great 
as  upon  a  hillside,  but  so  much  runs  off  that  the  soil  does 
not  receive  enough  to  supply  the  needs  of  the  plants.  Tf 


142 


FOOD 


the  ground  is  made  rough  and  porous  much  more  water 
will  be  absorbed  than  if  the  ground  has  been  left  smooth 
and  hard.  The  loosening  of  soil  so  that  it  may  catch  the 
rain  and  prevent  the  run-off  is  called  tilling. 

The  first  tilling,  in  preparing  the  soil  for  the  seeds, 
exposes  the  under  layers  to  the  action  of  the  air  and  also 
helps  to  bring  more  plant-food  to  the  surface.  Another 
necessity  for  tilling  is  to  put  the  soil  into  such  a  porous 
and  softened  condition  that  the  tender  roots  of  the  tiny 
plants  may  work  their  way  into  it.  Porous  soil  also 
allows  more  air  to  enter  it. 

All  tillage  of  the  soil,  after  the  seeds  have  been 
planted,  is  to  kill  weeds  and  to  save  the  moisture  which 
is  in  the  soil.  We  have  learned  that  water  moves 

through  the  soil  by  capillar- 
ity and  if  we  want  to  stop 
the  movement  we  must  close 
the  holes.  If  you  place 
some  powdered  sugar  upon 
a  cube  of  sugar,  as  shown  in 
the  illustration,  and  then 
touch  the  cube  to  some 
colored  water  (red  ink)  you 
will  see  the  water  rush  up 
the  cube  but  stop  when  it 
reaches  the  powdered  sugar. 
Capillarity  is  good  in  the 
cube  sugar  but  very  poor  in  the  powdered  sugar.  Try 
the  experiment.  We  can  do  the  same  thing  to  soil  by 
loosening  the  top  of  the  soil  and  making  it  fluffy  and 

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TILLING  THE  SOIL 


143 


powdery  just  like  the  powdered  sugar.  Such  a  layer  of 
loose  soil  is  called  a  mulch.  It  is  only  by  mulching  that 
the  moisture  can  be  kept  in  the  soil.  In  those  countries 
in  which  there  is  very  little  rain  in  summer  the  farmer 
is  able  to  raise  good  crops  by  the  proper  amount  of 
mulching. 

The  first  illustration  shows  that  soil  which  is  not 
mulched  cracks  open  and 
allows  evaportion  to  take 
place  far  below  the  sur- 
face. Soil  under  such 
conditions  will  dry  very 
quickly  and  be  of  no  use  for  farming.  The  second  illus- 
tration shows  soil  which  has  been  properly  mulched  and 

the  moisture  preserved. 
It  is  very  much  like  the 
cube  sugar  and.  the  pow- 
dered sugar:  the  lower 
soil  continues  to  bring  up 
water  from  below,  while  the  dry  mulch  prevents  its  loss 
when  it  comes  near  the  surface.  The  soil  must  be 
mulched  soon  after  each  rain,  as  the  water  opens  the 
pores  of  the  former  mulch  and  causes  it  to  be  of  no  use. 

Tilling,  as  has  been  noted,  kills  weeds.  This  is 
accomplished  by  the  tearing  up  of  the  weeds  and  saves  a 
large  amount  of  water.  Weeds,  like  other  plants,  use 
vast  quantities  of  water  but  they  give  no  return  to  the 
farmer.  Thus  all  the  water  which  weeds  use  is  a  total 
loss  to  the  farm.  Weeds  should  be  killed  for  other  reasons, 
the  chief  one  being  that  they  are  liable  to  kill  the  crops 
and  their  seed  or  stalks  may  spoil  some  crops. 


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144  FOOD 

56.     Irrigation  and  Drainage  of  Farms. 

It  often  happens,  in  lands  of  little  rain,  even  it 
the  soil  is  well  tilled  and  the  mulching  well  done,  that 
there  is  not  enough  water  in  the  soil  for  the  proper  needs 
of  the  crops.  Under  such  circumstances  it  is  necessary 
to  add  water  to  the  farm  from  some  river  or  well.  Any 
addition  of  water  to  land  is  called  irrigation.  The  soil 
should  always  be  tilled  as  soon  after  irrigating  as  it 
becomes  a  little  dry  on  top.  Why? 

Irrigation  is  of  the  utmost  importance,  since  about 
two-fifths  of  the  area  of  the  United  States  is  too  dry  for 
farming.  Up  to  the  present  time  a  little  over  ten  million 
acres  are  irrigated,  which  is  very  little  compared  with  the 
dry  area.  Proper  irrigation,  that  is,  where  there  are 
several  thousand  acres  to  be  irrigated,  must  be  under- 
taken by  the  government,  since  it  is  impossible  for  any 
place  to  build  a  large  irrigation  system.  Although  the 
cost  of  irrigation  is  great,  the  large  crops  more  than  pay 
for  it,  and  land,  which  otherwise  would  be  a  desert, 
blossoms  into  productiveness. 

Sometimes  there  is  too  much  water  in  the  soil  and 
it  is  necessary  to  remove  some  of  it.  This  removal  of 
water  from  land  is  called  drainage.  Drainage  may  be 
accomplished  by  ditches  and  by  covered  drain  pipes 
which  allow  the  water  to  enter  at  the  joints.  When  the 
pipes  are  used  the  drainage  is  called  underdrainage.  Un- 
derdrainage  is  better  than  surface  drainage  as  it  keeps 
the  water  at  the  proper  level  and  the  plants  send  their 
roots  deeper.  Thus  the  plants  have  more  soil  from 
which  to  obtain  their  food  and  therefore  they  grow  bet- 
ter. What  is  the  harm  of  having  too  much  water  in  the 
soil? 


GARDENING  145 

57.     Gardening. 

We  have  been  learning  about  plants  and  their  needs 
for  some  time  as  they  are  most  important,  since  all  life 
depends  upon  them.  Their  needs  have  been  learned  in 
the  various  topics  under  light,  heat,  air,  water,  and 
food.  We  have  seen  how  the  soil  must  be  treated  in 
order  to  supply  the  needs  of  the  plant  in  the  best  manner, 
and  to  preserve  the  water  which  is  in  the  soil.  Now  we 
should  put  our  knowledge  into  practice,  for  that  is  its 
real  test,  and  by  experimenting  we  may  strengthen  our 
knowledge,  and  also  increase  it.  This  experimenting 
should  be  performed  in  the  school  garden,  or  in  the  home 
garden,  or  what  is  best  of  all,  we  should  put  into  practice 
what  we  have  learned  about  plants  both  in  the  school 
garden  and  in  the  home  garden. 

The  selection  of  the  place  for  the  garden  is  very 
important.  It  should  be  near  enough  to  the  school  to  be 
convenient,  and  if  the  land  has  a  slight  slope  toward  the 
south  it  will  be  the  best  location  for  a  garden  in  which 
to  raise  some  of  the  early  crops.  Why  sloping?  Why 
toward  the  south?  Having  selected  a  good  location  what 
should  be  done  to  the  soil  before  planting  the  seeds? 
The  pulverizing  of  the  soil  should  be  done  to  a  depth  of 
at  least  six  inches  and  eight  inches  would  be  better. 

Even  if  the  land  has  not  been  used  as  a  garden  in 
former  years,  it  is  better  to  put  on  some  fertilizer  at  the 
same  time  as  you  are  breaking  up  the  top  of  the  soil.  The 
very  best  fertilizer  is  barnyard  manure.  A  good  way 
in  which  to  apply  the  manure  is  to  sprinkle  a  very  thin 
layer  of  it  on  the  soil  and  then  work  it  beneath  the  sur- 
face with  a  spade  or  fork.  Barnyard  manure,  in  addition 
to  being  an  almost  perfect  food  for  plants,  has  the  great 

Elem.Sci.  10 


146 


FOOD 


Cut   supplied   through    United    States  Department  of  Agriculture. 


GARDENING  147 

advantage  of  loosening  the  soil  and  making  it  more 
porous  .  Why  is  this  an  advantage?  Many  helpful 
bacteria  which  are  found  in  barnyard  manure  also  are 
added  to  the  soil.  If  barnyard  manure  cannot  be  easily 
obtained  a  small  amount  of  commercial  fertilizer  may  be 
used. 

You  should  always  sow  your  garden  seeds  in  rows. 
Straight  rows  make  a  garden  appear  neat.  You  can 
obtain  a  straight  line  by  means  of  a  tight  string.  Push 
a  stick  into  the  ground  where  you  want  to  begin  a  row 
and  tie  a  string  to  it.  Go  ro  the  other  end  of  the  row, 
drive  a  stick  and  tie  the  other  end  of  the  string  to  it. 
Where  did  you  use  a  tight  string  before?  Pows  should 
be  about  the  same  distance  apart  throughout  their  en- 
tire length.  This  can  be  accomplished  by  placing  the 
two  sticks  at  the  two  ends  of  the  second  row  the  same 
distance  from  where  they  were  for  the  first  row.  How 
deep  are  you  going  to  plant  your  seeds?  After  planting, 
the  soil  should  be  pressed  gently  down  s6  as  to  fit  closely 
around  the  seeds.  This  gives  them  the  best  chance  of 
obtaining  water  and  plant-food  from  the  soil. 

The  care  of  the  garden  is  chiefly  to  keep  it  moist,  but 
not  too  wet,  to  remove  the  weeds,  and  to  keep  the  upper 
part  of  the  soil  loose.  Can  you  give  the  reason  for  each 
of  these  necessities?  When  the  plants  come  up  they 
should  be  thinned,  that  is,  part  of  them  should  be  re- 
moved if  they  are  too  close  togther.  Each  plant  must 
have  room  in  which  to  grow  and  each  one  must  have 
plenty  of  sun.  Thinning  may  have  to  be  done  several 
times  as  the  plants  grow.  \Vhile  the  sunlight  is  neces- 
sary, some  plants,  especially  lettuce,  may  require  to  be 
shaded  by  boards,  placed  along  the  so.uth  side  of  the  row,. 


148  FOOD 

and  held  in  place  by  stakes    which  are    driven    into    the 
ground. 

The  illustration  gives  a  plan  for  a  garden  on  a  city 
lot,  about  fifty  by  ninety  feet,  and  shows  one  method  of 
following  early  crops  with  late  crops.  The  plan  will 
depend  upon  the  locality.  Full  directions  for  planting 
will  be  found  on  each  envelope  of  seeds*  You  have 
learned  in  general  what  to  do,  and  you  have  also  learned 
why  you  do  it. 


Review  Questions,  25. 

1.  What  effect  has  sunlight  upon    plants?        How 
can  you  prove  your  answer? 

2.  Are  there    any    plants,    either    large    or    small, 
which  are  harmed  by  sunlight?     Is  this  an  advantage  to 
us  or  is  it  a  disadvantage? 

3.  How  can  you  prove  that  plants  require  heat    in 
order  to  grow? 

4.  How  do  you  know  that  plants  need  air?     What 
part  of  the  air  do  the  leaves  take  in?     What  part  of  the 
air  do  the  roots  use?     Can  the  roots  take  this  part  of  the 
air  without  some  help?     Explain. 

5.  How  do  plants  help  man? 

6.  How  do  plants  obtain  the  water  which  they  need 7 
What  is  the  harm  of  too  much  water? 

7.  Do  all  plants  grow  in  the  ground?     Explain. 

8.  Tell  about  the  harmful  plants.     What  can  we  do- 
to  protect  ourselves  from  them? 

9.  Name  the  three  kinds  of  food'  material:  fop  man. 


REVIEW  QUESTIONS  149 

Give  some  examples  of  each  kind,  and  tell  the  use  of 
each  kind, 

10.  Explain  how  water  can  be  kept  in  the  soil. 
What  is  meant  by  'dry  farming"?  Is  the  farm  dry? 


Thus  far  in  our  science  work  we  have  been  learning 
about  the  necessities  of  life:  now  we  shall  study  some  of 
the  things  which  help  to  furnish  the  comforts  and  con- 
of  civilization. 


THE  GUIDE 


MECHANICS. 

58.     Simple  Measurement. 

The  first  -measurement  we  are  interested  in  is  that 
of  length.  We  want  to  know  how  tall  we  are,  how  high 
a  building  or  a  mountain  is,  and  how  far  it  is  to  a  cer- 
tain place.  When  you  say  that  you  are  four  feet  tall  you 
mean  that  you  are  four  times  as  long  as  the  foot  meas- 
ure. You  compare  your  length  with  this  length  which  is 
twelve  inches.  The  foot  measure  is  your  standard 
When  you  measure  the  length  of  a  building  you  find  how 
many  times  the  twelve  inches  are  contained  in  the  length 
of  the  building.  Thus  you  really  divide  the  length  of  the 
thing  you  are  measuring  by  the  length  of  the  standard. 
Where  the  comparison  of  two  objects  can  be  expressed 
as  numbers  the  comparison  is  always  division. 

Our  common  standards  of  length  are  the  foot,  yard, 
and  mile.  Other  countries  have  different  standards,  and 
we  are  gradually  coming  to  use  the  French  system.  The 
chief  advantage  of  the  French  system  is  that  it  is  a  deci- 
mal system.  Thus  10  millimeters  make  a  centimeter; 
10  centimeters  make  a  decimeter;  and  10  decimeters 
make  a  meter.  For  most  science  work  we  use  the 
centimeter.  There  are  no  eighths,  sixteenths,  and  other 
divisions  to  bother  us  in  our  work.  We  do  not  have  to 
remember  that  3  feet  make  a  yard,  and  that  5*/2  yards  or 
16J/2  feet  make  a  rod.  We  are  liable  to  forget  the  odd 
numbers  and  they  are  hard  to  multiply  and  divide.  The 


152  MECHANICS 

entire  French  system  is  decimal  as  we  shall  see  later  in 
our  science. 

The  next  measurement  after  length  is  area.  Area 
is  the  surface  of  the  thing  measured  and  is  found  by 
multiplying  the  length  by  the  width,  if  the  surface  has  all 
right  angles.  How  many  degrees  in  a  right  angle?  We 
express  area  in  square  feet,  square  yards,  or  square  miles. 
We  also  have  another  standard  called  the  acre.  Can  yon 
tell  how  many  square  feet  there  are  in  an  acre?  Not  an 
easy  number  to  remember,  is  it?  Many  of  our  standards 
are  not  very  convenient  but  we  do  not  think  much  about 
them  since  we  have  always  had  them.  It  is  only  when 
we  learn  of  a  better  method  of  doing  something  that  we 
realize  how  much  we  have  missed  up  to  that  time.  The 
French  acre,  while  it  is  about  two  and  one-half  times  as 
large  as  our  acre,  is  100  meters  long  and  100  meters  wide. 
This  makes  10,000  square  meters  and  is  much  more  easily 
remembered  than  the  number  of  square  feet  in  our  acre. 
For  science  work  we  use  the  small  measure  as  in  the  case 

of  length.     It  is  the  square  centimeter. 
-  Next  after  area  is  volume.       Volume  is  the 

space  occupied  by  a  solid  body  or  it  is  the 
space  within  a  hollow  body.  The  volume  of  a 
[sol  body  having  its  sides  at  right  angles  to  one 
(»1"|  another  can  be  obtained  by  multiplying  to- 
gether its  length,  width,  and  depth.  The  result 
is  expressed  in  cubical  measure,  such  as  cubic 
inches,  cubic  feet,  cubic  yards,  and,  in  the  case 
of  wood,  as  cords.  How  many  cubic  feet  in  a 
cord?  The  French  system  uses  the  cubic 
meter.  For  ordinary  science  work  we  shall 
use  the  cubic  centimeter.  A  measure  like  the 


MEASUREMENT  153 

illustration,  which    is    marked    in  cubic    centimeters    is 
called  a  graduate.     This  is  intended  for  liquids. 

When  we  are  using  the  French  system  we  should 
not  compare  it  with  the  English  standards  which 
we  use,  but  should  take  it  just,  as  it  is,  that 
is,  the  same  as  a  Frenchman  would  use  it.  How- 
ever, in  order  to  know  what  are  the  real  values  of  the 
French  units  you  should  learn  the  following:  1  centi- 
meter equals  .39  inch,  1  meter  equals  39.37  inches,  and  1 
kilometer  or  1000  meters  (the  French  mile)  equals  .62 
mile. 

Experiment  64. — Measurement. 

Apparatus :  Rule  one  foot  long,  marked  in  inches 
and  sixteenths,  and  in  centimeters  and  millimeters,  rec- 
tangular pieces  of  cardboard  of  various  sizes,  cubical 
blocks  of  wood  of  various  sizes,  empty  boxes  of  various 
sizes,  which  are  water  tight,  graduate,  several  circular  tin 
cans,  string. 

a.  Find  the  length  and  width  of  a  piece    of    card- 
board in  inches  and    sixteenths.        Now    find    the    area. 
Measure  the  same  piece  of  cardboard  in  centimeters  and 
millimeters.     Put  down  the  number  of  millimeters  to  the 
right  of  the  decimal  point.     Now  find  the  area.       Which 
is  easier  to  use,  the  French  system  or  the  English? 

b.  Measure  another  piece  of  cardboard,    using    the 
French  system  and  compare  its  area  with  the  area  of  the 
first  piece.     That  is,  divide  the  area  of  the  large  piece  by 
the  area  of  the  smaller  piece,  carrying  the  number  out  to 
two  decimal  points.       Now  measure  the  second  piece  of 
cardboard  in  the  English  system  and  compare    its    area 
with  the  area  of  the  first  piece,  also  in  the  English  sys- 


154  MECHANICS 

tern.  The  answer  should  be  nearly  the  same  but  there 
will  be  an  error  due  to  wrong  measurement.  You  see  it 
makes  no  difference  what  standards  you  use,  for  the  real 
size  of  the  body  remains  the  same.  Remember  the  two 
kinds  of  thermometers. 

c.  Find  the  volumes  of  two  blocks  of  wood  by  using 
the  French  and  the  English  systems.        When    you    get 
through  you  will  have  no    doubt    in    your    mind    which 
standards  are  the    easier    to    use.         Compare    the    two 
volumes.     How  much  larger  is  one  block  than  the  other? 

d.  Find  the  volumes  of  two  boxes,  in  the    French 
system  only.       Compare  the  two  volumes.        Using  the 
graduate,  see  how  many  cubic  centimeters  of  water    are 
required  to  fill  each  box.     How  do  these  amounts  com- 
pare with  the  answers  which  you  obtained  by  multiplica- 
tion? 

e.  Measure  the  diameter  of  a  circular  tin  can    and 
multiply  it  by  3  1-7  and  by  3.1416.      Then  measure  the 
distance  around  the  can  with  a  string  and  compare    the 
length  of  the  string  with  your  answer.     Which  is  more 
nearly  correct,  the  answer  obtained  by  multiplying    the 
diameter  by  3  1-7  or  by  3.1416? 

59.     Everything  has  Weight. — The  Balance. 

Whenever  we  try  to  lift  any  object  we  feel  a  '  pull 
which  we  must  overcome  if  we  are  to  move  it.  We  call 
this  pull  toward  the  earth  the  weight  of  the  object.  We 
say  that  the  force  of  gravity  pulls  the  object  and  the  earth 
together.  In  Section  63  we  shall  learn  more  about  forces. 
The  force  of  gravity  pulls  directly  toward  the  center  of  the 


EVERYTHING  HAS  WEIGHT  155 

earth,  and  unless  an  object  rests 
upon  something  it  will  fall  in  that 
direction.  If  we  wish  to  balance 
anything  so  that  it  will  stand  erect 
we  must  have  either  a  large  place 
upon  which  the  object  rests  or  we 
must  have  most  of  its  weight  be- 
low the  place  upon  which  it  rests. 
The  illustration  shows  you  how  you  ^_—___ 
can  balance  a  pencil  upon  its  point 
by  means  of  a  knife.  Explain  the 
reason  for  this. 

Since  everything  has  weight,  people  have  used 
weight  as  a  method  of  measuring  material,  for  a  long 
time.  v:  Just  as  there  are  standards  for  length,  area,  and 
volume,  So  there  are  standards  for  weight.  The  com- 
mon English  standards  are  the  pound  and  ton,  and  they 
have  no  special  meaning.  The  French  units  are  the 
gram  and  kilogram  (100  grams)  and  mean  something. 
The  gram  is  the  weight  of  one  cubic  centimeter  of 
water  at  4°C.  and  the  kilogram  is  the  weight  of  1000  cubic 
centimeters  of  water  at  4°C.  This  gives  two  ways  of 
measuring  water.  It  may  be  measured  in  a  graduate  or 
it  may  be  weighed.  The  number  of  cubic  centimeters 
and  the  number  of  grams  will  be  the  same.  In  the  Eng- 
lish system  the  weight  of  a  cubic  foot  of  water  is  62.4 
pounds  at  4°C.  There  is  no  connection  between  any 
two  parts  of  the  English  system  and  many  different  num- 
bers must  be  remembered  in  order  to  change  from  one 
unit  to  another.  The  French  system  of  weights  is  also 
decimal  and  there  is  nothing  to  remember.  The  weights 
are  always  expressed  in  parts  of  a  kilogram  or  parts,  of  a 
gram. 


156 


MECHANICS 


Experiment  65.— *Making  a  Balance   and  Weighing. 

Apparatus:  Hammer,  saw,  plane,  bit-stock,  bits 
y%"  and  *4",  sandpaper,  file,  pair  of  pincers,  set  of 
weights  (French  system). 

Materials:     Soft  pine  board  %"  thick,  12"  long  and 


*  Adapted  from  Farmers'  Bulletin  408.  U.  S.  Dept.  of  Agriculture 
Cut  supplied  through  United  States  Department  of  Agriculture. 


THE  BALANCE  157 

10"  wide,  another  board  X"  thick,  10"  long  and  4"  wide, 
two  nuts  having  a  half  inch  hole,  screw  eye,  four  Y% 
metal  screws,  iron  or  soft  brass  wire  No.  12,  pieces  of 
tin,  old  knife  blade,  one  dozen  ]/%"  screws  ^"  long,  fine 
needle. 

a.  The  illustration  shows  the  balance  as  it  should 
appear  when  finished.  The, base  (a)  is  12"x  7",  the  pil- 
lar (b)  is^;"  square  and  .9"  high,  and  is  set  in  a  J/£" 
hole  in  the  center  of  base.  The  upper  end  of  the  pillar 
should  be  sharpened  to  an  edge  as  shown  at  (k),  and  a 
slot  sawed  in  it  as  shown  at  (1).  The  beam  (c)  is  made 
from  a  stick  %"  square  and .10"  long.  Its  lower  edge  is 
left  straight  but  the  other. sides  are  planed  so  as  to  make 
the  ends  a  little  larger  than  half  an  inch  square.  The 
ends  are  then  rounded  so  that  the  nuts  (e)  will  screw  on 
snugly.  A  notch  1"  wide  and:^"  deep  is  cut  in  the  cen- 
ter of  the  bottom  edge.  This  receives  the  central  bearing 
of  the  beam.  An  inch  from  each  end  of  the  beam  a 
notch  J^"  deep  is  cut  to  receive  the  tray  bearings  (n). 
The  two  tray  bearings,  as  well  as  the  pillar  bearing, 
should  have  the  notches  lined  with  tin  as  shown  at  (m) 
and  (o),  A  pointer  (f)  made  of  J4"  material,  is  firmly 
fastened  to  the  beam  by  two  screws.  Its  lower  end  is 
provided  with  a  needle,  colored  black  so  as  to  be  easily 
seen.  The  screw  eye  (h)  is  placed  near  the  end  of  the 
pointer  and  in  the  center  of  the  pillar.  It  should  turn 
easily.  When  the  balance  is  completed,  turn  the  screw 
eye  so  as  to  hold  the  pointer  firmly,  then  paste  to  the 
pillar  back  of  the  pointer,  a  strip  of  water  paper  (g), 
bearing  scale  marks  1-16"  apart,  with  the  zero  mark  of 
the  scale  directly  back  of  the  needle. 

The  bearings  of  the  balance  are  the  most  important 


158  MECHANICS 

part  of  the  instrument.  The  knife  edge  (1)  may  be  made 
of  a  pocket  knife  blade  or  of  a  piece  of  hard  brass  filed 
to  a  straight  sharp  edge.  The  knife  edges  for  the  tray's 
bearings  (n)  are  made  by  filing  the  under  side  of  the  tray 
wires  where  they  cross  the  beam.  The  tray  wires  are 
made  of  No.  12  wire.  The  trays  (d)  are  3"x3"  and  J4" 
thick.  Two  holes  near  the  opposite  edges  receive  the 
wires  which  should  be  bent  in  the  opposite  directions  be- 
neath the  trays,  thereby  holding  them  firm  and  level. 
When  the  instrument  is  finished  it  may  be  made  to  bal- 
ance, that  is,  the  needle  may  be  caused  to  move  to,  and 
remain  at,  the  zero  point,  by  moving  the  nuts  on  the  ends 
of  the  beam  toward  the  lighter  side.  The  whole  instru- 
ment may  be  made  level  and  steady  by  means  of  the  four 
screws  at  the  corners  as  shown  in  the  illustration, 
although  this  is  not  absolutely  necessary.  A  paper  box 
(j)  may  be  used  for  small  objects.  The  other  tray  must 
have  an  equal  weight  placed  upon  it  and  the  instrument 
must  be  balanced  before  weighing  any  object. 

b.  Place  the  object  which  is  to  be  weighed,  upon  the 
lefthand  tray,  and  upon  the  righthand  tray  place  a  weight 
which  is  a  little  more  than  necessary.  Then  remove  this 
weight  and  put  on  the  next  smalkr  weight.  If  this  is 
too  little,  add  the  next  smaller  weight.  Continue  this 
until  the  instrument  balances.  The  pointer  must  always 
swing  free  of  the  screw  eye.  If,  instead  of  using  the 
large  weights  first,  the  small  ones  were  used  there  would 
be  no  small  ones  left  to  make  the  final  balance.  Always 
begin  with  the  large  weights. 


EVERYTHING  OCCUPIES   SPACE 


159 


60.     Everything  Occupies  Space. 

We  have  no  doubt  that  solids  and  liquids  occupy 
space  and  we  would  not  try  to  put  one  solid  in  the  space 
which  another  solid  is  occupying.  Yet  we  might  think 
that 'a  solid  could  be  placed  in  a  liquid  without  forcing 
the  liquid  away,  since  the  liquid  does  not  always  show 
that  its  surface  has  risen.  Do  you  remember  how  the 
crow  obtained  his  drink  of  water  from  the  deep  dish 
which  had  only  a  little  water  in  it?  Putting  one  kind  of 
material  in  the  place  of  another  is  called  displacement. 

It  is  very  hard  to  realize  that  gases  occupy  space  but 
they:  do,  as  we  shall  see  in  this  experiment. 

Experiment  66. — Displacement  of  Water  by  Solids 
and  Air. 

Apparatus:  Two  glasses,  stone,  block  of  wood, 
string,  funnel,  glass  tube,  rubber  tube,  large  bottle  or  jar, 
graduate,  rule. 

a.     Note  the  level  of  the  water  when  one  glass    is 


about  half  full  of  water,  and  then  lower  the  stone  as 
shown  in  the  illustration.  What  happens  to. the  level  of 
the  water?  Explain. 


160 


MECHANICS 


b.  Repeat,  using  a  block    of    wood.        Do    floating 
bodies  displace  any  water?     Do  they  displace  as  much 
as  they  would  if  they  sank? 

c.  Measure  the  block  of  wood  in  centimeters    and 
find  how  many  cubic  centimeters  it  contains.     Then  fill 
a  glass  completely  full  of  water,    place    the  glass  in    an 
empty  jar,  or  in  a  deep  saucer,  and  push  the  block  beneath 
the  surface  of  the  water  in  the  glass.       The  amount  of 
water  which  overflows  should  contain  very    nearly    the 
same  number  of  cubic    centimeters    as    you    have    just 
obtained  from  measuring  the  block.     Measure  the  water 
carefully  with  the  graduate  and  see  how  exactly  you  have 

performed  the  experiment.  Now 
you  can  tell  how  to  measure  the 
volume  of  a  stone  or  any  irregular 
body.  Explain. 

d.  Arrange  the  apparatus  as 
shown  in  the  illustration  and  push 
the  funnel  deeper  and  deeper  into 
the  water.  Does  the  water  go  up 
into  the  funnel?  Does  air  occupy 
space?  Can  you  explain  what 
happens  in  the  bent  tube? 


61.     Density. 

People  have  long  used  the  sayings  "As  heavy  as 
lead"  and  "Light  as  feathers"  without  meaning  just  what 
they  said.  They  really  meant  to  say  that  a  certain 
volume  of  feathers  is  much  lighter  than  the  same  volume 
of  lead.  When  we  tell  how  much  a  certain  volume  of  a 
material  weighs  we  are  giving  its  density.  Since  equal 


DENSITY  161 

volumes  of  feathers  and  lead  do  not  weigh  the  same, 
people  should  say  that  lead  has  a  greater  density  than 
feathers.  How  would  a  pound  of  feathers  compare  with 
a  pound  of  lead? 

We  are  often  more  interested  in  knowing  the  density 
of  materials  than  in  knowing  their  weight.  The  density 
can  always  be  obtained  by  dividing  the  total  units  of 
weight  by  the  total  units  of  volume,  and  is  expressed  as  so 
many  pounds  per  cubic  foot,  so  many  ounces  per  cubic 
inch,  or  so  many  grams  per  cubic  centimeter,  or,  in  fact,  in 
any  units  of  weight  and  any  units  of  volume.  Thus  we 
say  that  the  density  of  water  is  62.4  pounds  per  cubic 
foot  or  nearly  .6  of  an  ounce  per  cubic  inch,  or  1  gram 
per  cubic  centimeter.  Which  is  the  simplest  expression? 

Experiment  67. — Density. 

Apparatus:  Balance,  set  of  weights,  blocks  of  wood, 
pieces  of  stone,  brick,  lead,  iron,  zinc,  or  any  kind  of 
material  weighing  not  over '200  grams;  glass,  large  jar, 
graduate. 

a.  Weigh  each  object  and  make  a  record  of  the 
weights.  Find  the  volume  of  each  object  by  means  of  the 
displacement  of  water  and  record  the  volumes.  Divide 
the  units  of  weight  of  each  object  by  the  units  of  volume 
of  the  same  object.  This  gives  the  density  of  each  object. 

How  do  your  answers  compare  with  densities  which 
are  given  in  the  table?  If  they  are  not  quite  close,  repeat 
using  other  pieces  of  the  material. 

You  should  arrange  your  work  as  follows: 

Elem.  Sci.  1 1 


162 


MECHANICS 


Weight 
(in  grams) 


Name    of    object 

Aluminum   

Bone   _... 

Brass  . 

Cork  

Glass  4 m 

Iron 

Lead 

Pine  __... 

Stone  _.. 

Zinc  .. 


Volume  Density 

(in  cubic  (grams 

centimeters)  per  c.  c,) 

?  2,6 

?  1.9 

?  8.4 

•   ?  .24 

?  2.5 

?  7.7 
11.3 

?  .55 

?  2.6 

?  7. 


62.     Drawings, 

In  all  science  work  it  is  very  desirable  to  illustrate 
the  experiments,  which  you  write  upr  by  means  of  draw- 
ings. Drawing  is  like  writing,  since  we  use  both  to 
express  on  paper  the  ideas  which  we  wish  to  keep  in 
good  form,  but  drawing  is  often  a  better  means  of  expres- 
sion than  writing  as  it  sometimes  is  impossible  to  write,, 
or  even  explain  by  speecn,  some  idea  which  we  have. 
There  are  two  kinds  of  drawing;  that  made  without 
instruments  called  freehand  drawing,  and  that  made  with 
instruments  called  mechanical  drawing.  In  science  work 
mechanical  drawing  is  used  more  than  freehand  drawing, 


DRAWINGS       .  163 


The  chief  instruments  for  mechanical 
drawing  are  the  rule,  square,  triangle,  and 
compass.  A  cheap  kind  of  compass  is 
shown  in  the  illustration.  The  rule  is 
used  for  making  straight  lines,  the  .square 
for  forming  right  angles,  triangle  for 
obtaining  different  slants  or  angles,  and 
the  compass  for  drawing  circles  or  parts 
of  a  circle.  All  that  you  need  in  your 
science  work  is  a  rule  and  a  compass. 
The  longest  distance  across  a  circle  is  its 
diameter  and  the  distance  from  the  cen- 
ter of  the  circle  to  the  outside  of  the  circle 
is  called  the  radius. 

If  you  wish  to  make  copies  of  your 
drawings  the  following  experiment  shows 
one  method. 


Experiment  68. — Blue  Prints  from  Tracings. 

Apparatus:  Piece  of  window  glass  a  little  larger 
than  the  drawing  which  is  to  be  copied,  thumb  tacks. 

Materials:     Tracing  paper,  blue-print  paper. 

a.  Make  the  drawing  upon  any  kind  of  paper  and 
then  cover  it  with  a  piece  of  tracing  paper,  fastening  it 
with  thumb  tacks.  Trace  the  drawing  with  a  very  soft 
pencil  so  that  the  line  will  be  very  dark.  Use  the  rule 
and  compass  when  tracing  just  as  you  would  in  the  first 
drawing.  After  the  tracing  is  made,  place  a  piece  of 
blue-print  paper  upon  a  board  or  book  and  lay  the  trac- 
ing upon  it,  right  side  up.  Cover  both  with  the  piece 
of  window  glass  and  expose  to  the  sun  until  the  blue- 
print paper  has  become  a  bronze  color.  See  Experiment 


164  MECHANICS 

14  for  full  directions  for  the    use  of  blue  -  print    paper. 
Section  70  tells  how  to  make  blue-print  paper. 

Review  Questions,  26. 

1.  How  many  hours  of  sunlight  were  there  yester- 
day?    How  many  hours  without  sunlight  were  there  last 
night? 

2.  What  is  the  direction  of  sunset  now?     How  can 
you  tell  the  direction  of  sunrise  without  seeing  the  sun 
rise? 

3.  What  is  a  flame?      Prove  your  answer.       Why 
does  charcoal  burn  without  a  flame? 

4.  What  are  some  of  the    ways    of    keeping    food 
from  spoiling?     Which  is  the  worst  method?     Why? 

5.  Why  is  the  farmer's  occupation    the    most    im- 
portant?    Explain. 

6.  What  are  some  of  the  advantages  of  the  French 
system  of  measurement? 

7.  Explain  why  it  is  better  to  use  the  larger  weights 
before  using  the  smaller  ones  in  weighing. 

8.  When  you  blow    through    a  tube    into    a  liquid 
what  is  inside  the  bubbles?     What  does  this  show? 

9.  What  is  meant  when  it  is  said  that  the  density  of 
one  body  is  greater  than  that  of  another  body? 

10.  Besides  talking  and  writing,  how  else  can  you 
express  an  idea? 

63.     Forces. 

Any  push  or  pull  is  called  a  force.  Weight  is  a  pull 
between  the  object  and  the  earth  and,  as  we  have  learned, 
is  called  the  force  of  gravity.  When  we  say  that  a  body 
weighs  five  pounds  we  mean  that  the  pull  between  the 


FORCES  165 

body  and  the  earth  is  five  pounds.  It  would  be  neces- 
sary to  pull  the  body,  from  on  top,  with  a  force  of  five 
pounds,  to  keep  it  from  falling,  or  we  could  accomplish 
the  same  result  by  pushing  the  body  from  underneath. 
We  have  used  a  balance  to  find  out  the  weights  of  bod- 
ies. In  that  case  we  compared  the  weight  of  an  object 
with  the  weight  of  some  standard.  That  is  we  com- 
pared pulls. 

Some  bodies  move  as  a  whole,  that  is,  if  one  part  is 
pushed  or  pulled  so  that  it  moves  the  whole  of  the  mass 
moves.  Other  bodies,  such  as  rubber  and  thin  pieces  of 
many  kinds  of  material,  may  be  moved  in  one  part  while 
the  rest  remains  motionless.  If  we  fasten  a 
rubber  band  at  one  end  we  may  move  the 
other  end  a  considerable  distance  without 
causing  the  fastened  end  to  move.  When  the 
end,  which  has  been  moved,  is  released  it 
will  return  to  its  former  position.  Bodies 
which  act  like  this  are  elastic.  Thin  pieces  of 
wood  fastened  at  one  end,  may  have  the  othei 
end  bent  quite  a  distance  to  one  side  without 
breaking.  The  amount  of  stretching  or  bend- 
ing depends  upon  the  pull.  If  a  weight  of  five 
grams  bends  the  stick  or  stretches  the  rubber 
one  centimeter,  ten  grams  will  cause  a  move- 
ment of  two  centimeters.  This  gives  us  an- 
other method  of  weighing. 


Experiment  69. — Weighing  by  Elasticity. 

Apparatus:     Ring  stand,  spring    from    an 
old   window  roller,   or  some  brass   wire   No. 
20;  rule,  set  of  weights,  spring  balance  as  shown  in    the 
illustration,  string. 


166  MECHANICS 

a.  Fasten  about  six    inches    of    the    window-roller 
spring  to  a  ring  of  the  ring  stand  by  means  of  string  and 
bend  the  bottom  turn  of  the  spring  into  the  form  of    a 
hook.       Holding  the   rule  against  it,  hang  a  ten  gram 
weight  upon  the  spring  by  means  of  string.     How  much 
is  the  spring  stretched?       Hang  a  twenty  gram  weight 
upon  the  spring  and  see  how  much  the  total  stretch    is. 
Repeat  with  the  twenty  and  the  ten  together.  Does  the 
stretch  vary  with  the  pull?  Does  the  spring  always  return 
to  its  first  position  when  the  weights  are  removed?  If  you 
cannot   obtain    a   roller   spring   you    may    wind    enough 
brass    wire    upon     a     round     pencil     to     make     a     roll 
about  six  inches  long. 

b.  Examine  the  spring  balance.       Are  the  division 
marks  the  same  distance  apart?     Is  this  right?     Explain. 
When  you  weigh  anything  on  a  spring  balance  what  are 
you  really  measuring? 


A  pull  tends  to  separate  the  parts  of  a  body.  We 
say  we  can  pull  something  apart.  A  push  tends  to  make 
the  parts  of  a  body  closer  together  and  we  often  speak  of 
pushing  things  together.  When  we  push  the  parts  of  a 
body  closer  together  we  say  that  we  compress  the  body. 
Compression  requires  force  and  the  force  which  is  needed 
increases  with  the  surface  of  the  body.  It  takes  more 
force  to  compress  a  body  of  three  square  centimeters  of 
area  than  a  body  of  one  square  centimeter  of  area,  in  fact 
it  takes  three  times  as  much  force.  Yet  the  force  for  each 
square  centimeter  is  the  same  in  both  cases.  We  call 
the  force  per  unit  of  area  pressure.  The  pressure  needed 
to  accomplish  a  certain  compression  is  always  the  same 
for  the  same  body,  but  the  total  force  which  is  needed 
increases  with  the  area. 


THE  PLUMB-BOB  AND  THE  PENDULUM 


167 


64.  The  Plumb-bob  and  the  Pendulum. 
Since  the  force  of  gravity  acts  toward  the  center  of 
the  earth,  and  since  a  tight  string  makes  a  straight  line, 
we  can  easily  obtain  a  line,  which  if  con- 
tinued would  pass  to  the  center  of  the 
earth,  by  hanging  a  weight  on  ''he  end  of 
a  string.  This  is  called  a  plumb-bob  and 
the  direction  of  the  line  is  called  vertical. 
The  name  "plumb"  comes  from  the  Latin 
and  means  lead.  This  was  the  best  mate- 
rial for  plumb-bobs  in  olden  times.  We 
should  make  the  wall  of  our  buildings  ver- 
tical and  we  can  do  it  by  using  the  simple 
method  which  is  shown  in  the  illustration. 
As  you  have  learned,  the  surface  of 
water  is  level.  Another  name  for  level  is 
horizontal.  How  many  degrees  are  there 
between  a  horizontal  line  and  a  vertical 
line?  Float  a  piece  of  wood  upon  some 
water  in  a  dish  and  hang  a  plumb-bob  in 

the  water,  as  shown  in 
the  illustration.  Then 
measure  the  number 
of  degrees  there  are 
between  the  direction 
of  the  wood  and  the  di- 
rection of  the  plumb- 
line.  See  Section  81. 
If  we  swing  our 
plumb-bob  we  have  a 
--_  pendulum.  You  read 
in  Section  8  that  the 


168 


MECHANICS 


wheels  of  a  clock  are  allowed  to  turn  slowly  by  means  of 
a  pendulum.  Now  we  are  going  to  see  why  a  clock  can 
be  regulated  by  the  length  of  its  pendulum. 

Experiment  70. — The  Pendulum. 
Apparatus:     String,  stones  of  various  sizes,  rule, 
a.     Hang  up  a  small  stone    by    a    string    25    centi- 
meters long  and  count  the  number  of  swings  per  minute. 
Tie  on  a  large  stone  in  place  of  the  small  stone,  keeping 
the  length  of  the  pendulum  the  same.     Does  the  weight 
of  the  stone  make  any  difference  in  the  number  of  swings 
per  minute?     The  time  that  it  takes  a  pendulum  to  swing 
from  one  side  and    return    again    to  its 
first     position    is     called    the     time    of 
vibration. 

,*  b.  Hang  up  a  stone,  making  the 
•I  string  100  centimeters  long  and  count 
the  vibrations  per  minute.  How  does 
the  number  compare  with  the  result 
obtained  in  (a)  above?  If  you  want  a 
clock  to  go  faster  would  you  lengthen 
or  shorten  the  pendulum?  The  illustra- 
tion shows  a  clock  pendulum.  The  pend- 
ulum is  kept  in  motion  by  the  push  o/ 
the  projections  on  the  wheel,  but  the 
time  is  regulated  by  the  length  of  the 
pendulum.  Do  you  think  that  a  clock 
would  go  faster  or  slower  in  hot 
weather?  Explain.  See  Section  18. 

65.     The  Lever. 

A  stick,  supported  at  a  point  between 


THE  USE  OF  THE  LEVER  169 

its  ends,  is  called  a  lever.  The  point  of  support  is  namrti 
the  fulcrum.  The  advantage  of  the  lever  is  to  obtain  a 
large  force  by  the  use  of  a  small  force.  Let  us  learn  by 
experimenting. 

Experiment  71. — The  Use  of  the  Lever. 

Apparatus:  Long  rule,  or  stick  marked  with  equal 
divisions,  triangular  piece  of  wood  to  serve  as  a  fulcrum, 
set  of  weights. 

a.     Arrange  the  apparatus  as  shown  in  the  illustra- 


1111 A  ...  I  ....... 

I  •     -         I 

tion.  Does  it  balance?  Multiply  the  smaller  weight  by 
its  distance  from  the  fulcrum  and  compare  the  result 
obtained  by  multiplying  the  larger  weight  by  its  distance 
from  the  fulcrum.  It  is  not  safe  to  draw  your  conclu- 
sions, or  form  an  opinion  from  one  experiment.  There- 
fore place  these  two  weights,  and  also  other  weights,  at 
different  distances  from  the  fulcrum  so  that  they  balance 
and  compare  the  products  as  suggested  above.  What 
are  vour  final  conclusions? 


This  experiment  shows  you  how  you  can  use  a  small 
force  on  the  long  arm  o£  a  lever  and  exert  a  large  force 
on  the  short  arm.  Notice  that  the  small  force  has  to  act 
a  greater  distance  than  tfie  large  force.  You  have  seen 
men  lift  large  rocks  out  of  the  ground  by  means  of  bars 
of  iron  called  crowbars.  You  use  a  lever,  or  two  of  them, 


170 


MECHANICS 


when  you  cut  cloth  or  use  a  nutcracker.  Where  is  the 
easiest  cutting  done,  near  the  fulcrum  or  at  the  tip  of  the 
scissors?  If  you  want  to  crack  a  hard  nut  where  in  the 
nutcracker  do  you  place  it?  The  lever  is  called  a  ma- 
chine since  it  enables  man  to  use  a  small  force  to  over- 
come a  large  force.  It  is  the  simplest  machine  we  have 
and:  has  been  known  for  countless  centuries.  See  Sec- 
tion 80. 


66.     The  Inclined  Plane. 

r  • 

Another  machine  which  is  very  simple  and  has  been 
known  as  long  as,  if  not  longer  than,  the  lever  is  the 
inclined  plane.  This  is  simply  a  board  with  one  end 
higher  than  the  other.  Instead  of  lifting  a  weight  verti- 
cally it  is  pushed  or  rolled  up  the  slanting  board.  Since 
the  force  acts  a  longer  distance  up  the  plane  it  is  not  as 
great  as  it  would  be  if  it  acted  only  vertically.  How  is 
this  like  the  lever? 

Experiment  72. — The  Use  of  the  Inclined  Plane. 

Apparatus :  As 
shown  in  the 
illustration,  rule. 

a.  Find  the 
weight  of  the  car 
with  its  load  of 
stones  or  weights. 
Find  the  force 
which  i  s  neces- 
sary to  pull  the  car  up  the  inclined  plane.  Which  is 
greater? 


THE  INCLINED  PLANE  AND  WEDGE  171 

b.  Make  the  inclined  plane  steeper  or  less  steep  and 
find  the  pull  necessary  to  pull  the  car  up  it.  Measure  the 
length  of  the  plane  and  the  height  of  the  high  end  of  the 
plane.  Multiply  the  pull  up  the  plane  by  the  length  of 
the  plane  and  compare  it  with  the  result  obtained  by 
multiplying  weight  of  the  car,  with  its  load,  by  the  height 
of  the  end  of  the  plane.  Should  you  draw  your  conclu- 
sions from  this?  Finally  draw  your  conclusions.  Cm 
you  see  any  relation  between  the  lever  and  the  inclined 
plane? 


A  very  common  use  of  the  inclined  plane  is  made  in 
splitting  stumps.  The  inclined 
plane  in  this  case  is  called  a 
wedge.  Instead  of  anything 
moving  up  the  inclined  plane  the 
inclined  plane,  the  wedge,  moves 
and  the  material  has  to  separate 
as  the  wedge  is  driven  into  it. 
The  advantage  is  just  the  same 
as  in  the  last  experiment.  Many  ^? 
other  machines  are  very  much 
like  the  lever  and  the  wedge,  although  they  are  given 
other  names.  We  shall  learn  more  about  machines  next 
year,  but  it  is  most  important  to  know  just  how  these  two 
aid  us. 

Review  Questions,  27. 
1.     Why  is  the  image  of  an  object  in  a  mirror  right 


172  MECHANICS 

side  up,  but  in  a  pinhole  camera  upside  down? 

2.  What  are  the  sources  of  heat  and  light?  Can  you 
obtain  heat  without  light,  or  light  without  heat? 

3.  What  is  a  porous  body?     Can  it  be  changed  so 
as  not  to  be  porous?      Is  there  any  advantage  in  having 
bodies  porous?     Name  one  very  important  porous  body. 

4.  Name  all  the  uses  of  water. 

5.  What  should  we  do  if  we  wish  to  keep  in  good 
health? 

6.  If  a  clock  is  going  too  slowly,  what  should  you 
do  to  regulate  it?     Explain. 

7.  What  is  a  force?     What  can  forces  do? 

8.  Name  two  ways  by  which  you  can  exert  a  large 
force  by  using  a  small  force. 

9.  What  effect  have   forces  upon    elastic    bodies? 
What  use  is  made  of  this  effect? 

10.  What  are  machines?       What    are  the    uses    of 
machines? 


THE  GUIDE 


MAGNETISM  AND  ELECTRICITY. 


67.     The  Lodestone. 

There  are  two  kinds  of  material  which  have  the 
power  of  pulling  bits  of  iron  to  them  without  first  touch- 
ing the  iron.  These  are  called  magnets.  There  are 
natural  magnets  and  magnets  which  have  been  made  by 

man.  The  illustration  shows  a 
piece  of  natural  magnet  which 
has  attracted  iron  filings  to  its 
two  ends.  Natural  magnets  are 
black  stones  and  were  first  found  near  Magnesia  in  Asia 
Minor.  A  natural  magnet  is  called  a  lodestone.  The 
word  "lodestone"  means  leading  stone,  for  if  a  piece  of 
lodestone  is  hung  up  by  a  fine  thread,  one  end  will  point 
nearly  north,  and  thus  the  lodestone  will  direct  or  lead 
us.  The  ends  of  the  lodestone  where  the  iron  filings  are 
the  thickest,  are  called  its  poles.  The  poles  ire  named 
north  and  south  because  one  will  point  north  and  the 
other  will  point  south.  The  poles  of  a  magnet  attract 
iron  with  greater  force  than  any  other  part  of  the  mag- 
net. Lodestones  are  not  important  and  are  interesting 
only  because  they  were  the  first  magnets  which  were  dis- 
covered by  man,  and  their  mysterious  power  has  never 
been  fully  understood. 


MAGNETIC  MATERIALS  175 


68.     Steel  Magnets. 


Magnets  which  are  made  by  man 
are  called  artificial  and  are  much 
stronger  than  the  natural  magnets. 
All  artificial  magnets  are  made  from 
steel.  A  straight  magnet  is  called  a 
bar  magnet,  while  a  straight  bar, 
which  has  been  bent  into  the  form 
of  a  horseshoe,  is  called  a  horseshoe 
magnet.  The  illustration  shows  a 
horseshoe  magnet.  The  chief  ad- 
vantage of  this  form  is  that  both 
poles  can  pull  upon  or  attract  the 
same  piece  of  iron.  The  piece  of 
iron,  which  is  shown  across  the 
poles  of  the  horseshoe  magnet,  is 
called  a  keeper.  It  retains  or  keeps 
the  magnetic  strength. 


Experiment  73. — Magnetic  Materials. 

Apparatus:  A  bar  magnet,  pieces  of  every  kind  of 
material  you  can  find,  sheet  of  paper,  thin  piece  of  wood, 
piece  of  window  glass  and  any  sheet  metal. 

a.  Try  to  pick  up  pieces  of  every  kind  of  material 
with  your  magnet.  What  can  you  pick  up  with  it?  If 
you  try  to  pick  up  a  piece  of  tin  with  the  magnet  you 
must  remember  that  "tin"  is  iron  covered  with  tin.  Iron 
is  sometimes  covered  or  plated  with  copper  and  brass. 
What  are  your  final  conclusions  in  regard  to  the  kind  of 
material  which  is  attracted  by  a  magnet? 


176  MAGNETISM  AND  ELECTRICITY 

b.     See  if  the  magnetism  will  pass  through  a  piece  of 
paper,  thin  wood  or  thin  glass,  or  thin  sheets  of  metal. 


The  space  around  a  magnet,  in  which  there  is  mag- 
netism, is  called  a  magnetic  field.  The  magnetic  field  ^ 
strongest  near  the  poles.  The  magnetic  field  may  be 
drawn  in  the  following  way: 

Experiment  74. — To  Draw  a  Magnetic  Field. 
Apparatus:     Bar  magnet,  iron  filings  in  salt  sifter. 

Materials:     Piece  of  paper. 

a.  Lay  the  magnet  upon  a  table,  cover  it  with  the 
piece  of  paper,  and  slowly  sift  the  iron  filings  upon    the 
paper.     They  will  take  certain  positions  and  they  may  be 
aided  in  arranging  themselves  by  jarring  the  table  a  little. 
Draw  with  a  soft  pencil  a  large  number  of  lines,  following 
as  closely  as    possible    the    lines    which    the    filings    are 
taking.     After  drawing  the  lines  return  the  filings  to  the 
sifter. 

b.  Hide  the  drawing    and  make    another    drawing 
from  memory.       Then  compare  your  two  drawings  and 
see  what  you  have  omitted.     You  should  learn  to  draw  a 
magnetic  field  from  memory. 


MAGNETIC    FIELDS 


177 


Just  as  you 
made  blue 
prints  of  leaves 
and  small  ob- 
jects, and  cop- 
i  e  d  drawings, 
so  you  can  ob- 
tain blue  prints 
o  f  magnetic 
fields.  The  il- 
lustration gives 
one  example  of 
a  magnetic  field.  You  can  make  many. 

Experiment  75. — Blue  Prints  of  Magnetic  Fields. 

Apparatus:     Two   bar  magnets,    piece    of    window 
glass,  iron  filings  in  a  salt  shaker. 

Materials:     Blue-print  paper. 

a.  Lay  the  two  magnets  upon  a  book,  side  by  side, 
about  the  width  of  the  magnets  apart,  having    the    two 
north  poles  pointing  in  the  same  direction.     Lay  a  piece 
of  blue-print  paper  upon  the  magnets  with  the  yellow  side 
up.     Keeping  in  the  shade,  sprinkle  iron  filings  upon  the 
paper  as  in  the  last  experiment.     When  the  filings    are 
nicely  arranged  cover  them  carefully  with  the  piece  of 
window  glass,  and  place  in  the  bright  sunlight.       When 
the  paper  has  changed  to  the  familiar  bronze,  return  the 
filings  to  the  shaker  and  immediately  wash  the  blue  print 
in  water. 

b.  Repeat  (a)  above,  but  have  the  north  pole  of  one 
magnet  and  the  south  pole  of  the  other  magnet  pointing 
the  same  way.     After  the  blue-print  is  made  compare  it 


Elem.  Sci.  12 


178 


MAGNETISM  AND  ELECTRICITY 


with  the  other  blue  print.  Notice  that  the  lines  of  force, 
as  the  filing  are  said  to  indicate,  seem  to  push  against 
one  another  in  (a)  and  pull  upon  one  another  in  (b). 


So  far  we  have  noticed  that  magnets  attract  iron. 
Now  we  are  going  to  learn  about  the  effect  which  two 
magnets  have  upon  each  other. 

Experiment  76. — Attraction  and  Repulsion. 
Apparatus:     Two  bar  magnets,  stand. 
Materials :     Thread,  heavy  paper, 
a.     Make  a  support  for  one  magnet  from  the  paper 

and  hang  it  up  by 
the  thread,  as  shown 
i  n  the  illustration. 
The  thread  will  un- 
twist but  the  magnet 
will  finally  come  to 
rest.  Then  bring  up 
one  pole  of  the  other 
magnet  to  one  pole  of 
the  supported  mag- 
net. What  happens? 
The  magnets  have 
their  north  poles  marked.  Which  poles  caused  the 
result?  Now  bring  the  other  pole  to  the  same  pole  of 
the  supported  magnet  and  tell  what  happens.  As  we 
have  learned,  if  the  poles  come  together  it  shows  attrac- 
tion ;  if  they  go  away  from  each  other  we  call  it  repul- 
sion. What  is  the  rule  for  attraction  and  repulsion? 


INDUCED   MAGNETISM  179 

The  illustration  shows  an  experiment  which  you 
should  repeat  for  yourself. 
Take  a  nail  and  hold  it  near  a 
magnet  but  not  touching  it. 
The  nail  will  then  attract  iron 
filings.  Remove  the  magnet 
and  the  nail  loses  its  magnet- 
ism. Magnetism  which  is 
caused  in  this  manner  is  called 
induced  magnetism.  Magnet- 
ism must  be  induced  in  an  object  before  it  can  be 
attracted  by  a  magnet.  Since  iron  is  the  only  common 
material  which  can  have  magnetism  induced  in  it,  it  is 
the  only  common  metal  which  can  be  attracted.  Steel 
is  made  from  iron  and  retains  its  magnetism  better  than 
iron  because  it  is  harder.  Electricity  can  produce  in 
iron  much  stronger  magnetism  than  can  exist  in  steel 
magnets.  We  shall  learn  about  this  next  year. 

Review  Questions,  28. 

1.  What  are  the  advantages  of  sunlight? 

2.  What  is  the  proper  method    of    heating    water, 
from  above  or  from  below?     Explain. 

3.  How  do  fishes  live  in  the  water?     Do  plants  help 
fishes?     Do  plants  help  man?     Explain  fully. 

4.  Why  do  we  eat?     Why  do  wre  drink?     When  do 
we  need  to  eat  fat?     When  do  we  need  to  drink  a  large 
amount  of  water? 

5.  Name  some  plants  which  are  harmful    to    man. 
What  can  we  do  to  prevent  these  plants    from    harming 
us? 


180  ELECTRICITY  AND  MAGNETISM 

6.  Name  all  the  advantages  of  tilling  the  soil  and 
tell  how  tilling  may  be  accomplished. 

7.  What  is  a  machine?     Of  what  use  is  a  machine 
to  us?     Name  two  simple  machines  and  explain  how  they 
help  us. 

What  are  magnets?       What  are  the  two    kinds    of 
magnets?    What  is  meant  by  attraction? 

9.  What  are  the  poles  of  a  magnet?     How  are  the 
poles  of  a  magnet  different  from  the  rest  of  the  magnet? 
What  are  lines  of  force? 

10.  What  is    a  keeper  and  what  is  its  use?     What 
is  a  magnetic  field?     WThat  is  meant  by  repulsion?  What 
is  induced  magnetism? 


THE  GUIDE 


*THE  ARTS  AND  INDUSTRIES. 


69.     Weather  Observations. 

The  observation  of  the  weather  is  valuable  for  many 
reasons.  If  we  make  observations  regularly  we  get  into 
the  habit  of  keeping  records  of  the  observations  in  order 
to  compare  them  with  later  ones.  We  soon  learn  that 
our  memory  is  often  weak  and  that  records  are  to  be 
trusted  every  time.  The  value  of  the  records  grows  as 
they  increase.  Thus  a  record  of  the  daily  temperature 
for  two  years  is  much  more  valuable  than  for  one  year, 
while  a  record  for  ten  years  is  of  great  value,  especially 
in  a  farming  district.  Why?  In  the  same  way  the  rec- 
old  of  the  rainfall  for  several  years  helps  the  farmers,  for 
they  would  not  plant  crops  which  require  a  very  large 
amount  of  water  in  a  locality  where  the  rainfall  is  always 
small. 

The  records  which  you  are  beginning  to  keep  will 
become  a  source  of  great  pleasure  to  you  as  you  grad- 
ually add  more  observations,  and  the  record  for  each 
kind  of  observation  increases  with  time.  Begin  by 

*  Note  to  the  Teacher: — The  scientific  facts,  upon  which 
the  following  practical  applications  are  based,  have  been  stud- 
ied in  the  preceding  divisions.  The  great  purpose  of  this 
division  is  to  show  that  science  is  a  matter  of  everyday  interest 
and  is  of  immense  value  to  everyone  alike.  Since  the  prin- 
ciples have  been  stated  in  other  sections  these  sections  are 
necessarily  shorter  than  those  others. 


MOW  TO  MAKE  BLUE-PRINT  PAPER  183 

arranging  your  records  in  orderly  columns.  As  time 
goes  on,  the  arrangement  in  columns  permits  an  easy 
reference  to  past  observations,  and  all  the  records  of  the 
same  kind  are  together.  The  government  of  the  United 
States  is  continually  making  records  of  the  weather  and 
these  observations  save  millions  of  dollars  every  year  to 
farmers  and  ship  owners. 

70.  How  to  Make  Blue-Print  Paper. 
While  blue-print  paper  may  be  purchased  at  a  small 
price,  it  is  often  desirable  to  prepare  certain  kinds  of 
paper  so  that  prints  may  be  made  on  them.  Another 
use  of  the  mixture  is  to  apply  it  to  cloth.  Simple  cotton 
cloth  soaked  in  it  may  be  printed  upon  in  the  same  man- 
ner as  upon  paper.  A  collection  of  prints  of  leaves  may 
be  made  and  the  different  pieces  .may  then  be  sewed 
together  to  form  a  pillow  cover.  The  solutions  should  be 
made  as  follows: 

Solution  A.     Distilled  water  125  cubic  centimeters.* 
Potassium  Ferricyanide  25  grams. 
Gum  Arabic  2  grams. 

Solution  B.     Distilled  water   125  cubic  centimeters. 
Iron — ammonia  citrate  37  grams. 
Gum  Arabic  2  grams. 

Use  equal  parts  of  A  and  B,  mixing  them  only  in  the 
dark.  Candle  light  may  be  used.  The  two  solutions  are 
not  affected  by  light  until  they  are  mixed.  Paper  which 
has  no  coating  upon  it  should  be  used.  The  mixture  may 
be  applied  in  two  ways — it  may  be  poured  upon  the  paper 

*  See  Sections  58  and  59  for  information  in  regard  *o 
measuring  and  weighing. 


184  THE  ARTS  AND  INDUSTRIES 

and  the  excess  allowed  to  drip  off,  or  it  may  be  applied 
by  means  of  a  swab  of  cotton  upon  a  little  stick.  The 
paper  must  be  allowed  to  dry  in  the  dark  before  being 
used.  It  is  best  not  to  prepare  any  more  paper  than  will 
be  used  within  a  few  days,  as  it  spoils  quite  quickly. 

It  is  not  necessary  to  cover- the  whole  of  a  piece  of 
paper  if  the  print  is  to  be  a  small  one  upon  a  large  sheet 
of  paper.  Merely  apply  the  mixture  where  it  is  needed. 

71.     Solar  Heaters. 

In  Experiment  22  it  was  noticed  that  black  and  rough 
materials  become  much  warmer  in  the  sun  than  do  other 
objects.  Man  has  made  use  pf  this  knowledge  by  making 
the  sun  warm  water  for  him.  If  many  feet  of  water  pipe 
are  painted  black  and  exposed  to  the  heat  of  the  sun 
the  water  within  them  will  become  quite  hot.  This  is 
a  simple  solar  heater.  The  longer  the  pipe  the  more 
water  can  be  heated  at  one  time.  Man  has  learned 
something  else  about  the  heat  from  the  sun.  If  a  box  is 
made  of  wood,  painted  black  inside,  and  covered  with 
glass,  the  heat  which  is  received  from  the  sun  can  enter 
the  box  but  cannot  get  out  again  as  rapidly.  Thus  the 
temperature  inside  the  box  rises  much  higher  than  the 
temperature  outside,  if  the  sun  is  shining.  Now  if  such 
a  box  is  filled  with  many  feet  of  water  pipe,  the  water 
which  is  inside  the  pipe  will  become  very  hot.  Such  a 
heater  on  a  sunny  day  can  raise  the  temperature  of  water 
hieh  enough  for  a  hot  bath.  The  water  from  a  solar 

J>  o 

heater  does  not  have  to  be  heated  very  much  in  order  to 
make  it  boil,  so  for  cooking  purposes  it  causes  a  saving 
in  fuel. 


HOT-AIR  ENGINE— FIREPROOFING 


185 


A.r 


72.     Hot-Air  Engines. 

If  air  is  heated  it  expands,  as  was  learned  in  Section 
18.  This  principle  has  been  used  to  obtain 
power.  The  illustration  shows  a  very  sim-  j 
pie  hot-air  engine.  If  a  tube  is  closed  at 
one  end  and  has  the  other  end  sliding,  which 
is  called  a  piston,  when  the  air  inside  is 
strongly  heated  by  a  Bunsen  burner  it.  will 
expand  and  force  the  piston  out.  After  re- 
moving the  burner  the  air  will  cool  and  con- 
tract and  the  piston  will  return  to  its  first 
position.  This  is  the  principle  of  the  hot- 
air  engine  but  the  usual  engine  has  many 
more  parts,  and  the  hot  air  is  exchanged  for  cold  air 
instead  of  waiting  for  the  hot  air  to  become  cold.  You 
know  now  why  the  engine  works.  To  learn  just  how  it 
works  will  require  further  study  after  you  have  had  more 
about  machines. 

73.     Fireproofing. 

Some  materials  burn  much  more  easily  than  others 
and  the  same  kind  of  material  burns  more  easily  if  il  is 
opened  up  to  the  effect  of  the  air  than  if  it  is  tightly  rolled 
or  compressed.  The  reason  for  this  is,  that  if  a  body  is 
porous  the  oxygen  of  the  air  can  get  at  more  of  the  mate- 
rial at  one  time  and  more  burning  or  combustion  can  take 
place.  Since  this  is  so,  if  we  wish  to  make  some  mate- 
rial less  easy  to  burn  we  must  put  something  upon  it 
which  will  keep  away  the  air  from  its  surface.  A  solu- 
tion which  contains  tin,  or  a  solution  of  water  glass,  will 
accomplish  this  purpose  quite  well  without  harming  the 
material. 


186  THE  ARTS  AND  INDUSTRIES 

It  must  be  remembered,  however,  that  nothing  which 
can  burn  can  be  made  really  fireproof.  If  the  temper- 
ature is  raised  high  enough  the  material  will  burn  or  be 
destroyed,  no  matter  what  is  upon  it.  Fireproofing 
serves  to  prevent  easy  burning  and  on  that  account  is  a 
very  valuable  process. 

74.     Waterproofing. 

Many  substances  are  more  or  less  porous  and  allow 
water  to  penetrate  them.  As  we  learned  in  Experiment 
46,  water  may  be  kept  out  of  material  by  stopping  the 
pores.  In  that  experiment  paraffin  was  used  but  there 
are  other  somewhat  similar  materials  which  may  be  used 
in  the  same  manner.  Thus  if  the  pores  of  cloth  are  filled 
with  rubber  we  obtain  what  we  call  rubber  cloth.  Oil- 
cloth and  oilskins  are  other  examples  of  the  filling  of 
pores  of  cloth.  The  foundations  and  cellar  floors  of 
buildings  may  be  made  waterproof  by  covering  them 
with  melted  tar,  or  tar  paint;  by  asphalt,  and  by  the 
addition  of  other  matter  to  the  concrete  before  it  is 
mixed. 

Another  very  interesting  method  is  to  have  the  pores, 
but  treat  the  cloth  in  such  a  way  that  water  will  not  read- 
ily enter.  The  following  experiment  shows  the  prin- 
ciple which  underlies  this  method. 

Experiment  77. — Waterproofing. 

Apparatus:  Burner,  ring  stand,  wire  gauze,  tin 
dish,  small  glass  tube,  glass. 

Material:     Paraffin. 

a.  Insert  the  glass  tube  in  some  water  in  the  glass 
and  note  how  high  the  water  goes  by  capillarity.  See 
Section  41. 


WATERPROOFING  187 

b.  Melt  some  paraffin  by  gentle  heat  and  dip  the 
tube  into  it.  Warm 'the  tube  gently  until  the  paraffin  is 
spread  in  an  invisible  layer  up  inside  it,  without  stopping 
the  hole.  This  makes  the  hole  smaller  and  you  might 
expect  that  the  water  would  go  higher  in  it.  When  the 
tube  is  cold  place  it  in  the  water.  Where  is  the  surface 
of  the  water  inside  the  tube? 


This  is  the  principle  by  which  raincoats  keep  out  the 
rain.  The  goods  are  porous  but  there  has  been  produced 
a  change  in  the  threads  so  that  capillarity  has  been  de- 
stroyed. It  is  impossible  to  wet  anything  beneath  the 
surface  unless  capillarity  acts.  Why  do  you  wet  a  mop 
before  using  it? 

75.     Flavoring  Extracts  and  Perfumes. 

The  making  of  flavoring  extracts  and  perfumes  are 
examples  of  solution  by  special  solvents.  In  this  case 
alcohol  is  the  solvent.  Vanilla  extract  may  be  made  by 
grinding  vanilla  beans  in  a  meat  chopper  and  allowing 
the  mass  to  soak  in  a  mixture  of  one-half  pure  alcohol 
and  one-half  distilled  water,  in  a  stoppered  bottle  for 
several  days.  A  small  amount  of  sugar  may  aid  the 
solution.  This  will  produce  a  delicately  flavored  extract 
at  a  moderate  price. 

Grate  off  the  outside  of  several  lemons,  or  oranges, 
and  soak  the  gratings  for  several  days  in  pure,  undiluted 
alcohol  if  you  wish  to  make  lemon  or  orange  flavoring 
extracts  at  a  slight  price. 

Many  perfumes  may  be  made  by  allowing  the  mate- 
rial, whose  perfume  is  desired,  to  soak  for  several  days  in 


188  THE  ARTS  AND  INDUSTRIES 

pure  undiluted  alcohol.  All  of  these  solutions  must  be 
kept  in  tightly  covered  bottles  as  the  alcohol  will  rapidly 
evaporate  if  the  bottles  are  left  unstoppered. 

76.     To  Remove  Grease  Spots  and  Stains. 

We  may  make  use  of  both  solution  and  capillarity 
for  the  removal  of  grease.  In  addition  to  the  solvents 
which  are  mentioned  in  Section  36  there  are  ammonia 
water,  naphtha,  benzine,  and  ether  for  the  removal  of 
grease.  All  but  ammonia  water  are  very  dangerous  to 
use  as  they  are  so  easily  set  on  fire.  Grease  can  also  be 
removed  by  means  of  a  hot  iron.  Place  a  cloth  or  blot- 
ting paper  under  the  goods,  cover  the  goods  with  a  cloth 
or  a  piece  of  paper,  and  press  with  a  moderately  hot  iron. 
The  heat  melts  the  grease  and  weakens  the  capillarity  so 
that  the  grease  moves  away  from  the  heat. 

Ink  spots  may  be  removed  by  salt  and  lemon  juice 
if  the  spots  have  not  become  dry.  Red  ink  may  be 
removed  by  ammonia  water.  Paint  may  be  removed  by 
turpentine  and  benzine.  Tea  and  coffee  stains  may  be 
removed  by  cold  water  and  glycerine  if  allowed  to  soak 
for  several  hours.  Enameled  sinks  and  bathtubs  may  be 
cleaned  with  kerosene,  followed  by  hot  water  and  soap. 

77.     How  to  Make  Soap. 

There  are  two  kinds  of  soap  —  hard  and  soft.  In 
olden  days,  before  soap  became  so  common  and  so  cheap, 
soapmaking  was  one  of  the  household  arts.  Then  there 
was  much  soft  soap  made  as  it  was  easily  made  and  con- 
venient to  use.  Now  hard  soaps  of  various  kinds  have 
nearly  driven  this  art  from  the  home. 


SOAP  MAKING  189 

Soap  is  a  combination  of  grease  and  lye.  Caustic 
potash  and  grease  make  soft  soap,  while  caustic  soda  and 
grease  make  hard  soap.  The  kind  of  grease  which  is 
used  makes  the  soap  high  grade  or  low  grade ;  toilet  soap 
or  laundry  soap. 

Experiment  78. — Soap  Making. 
Apparatus:     Burner,  ring  stand,  tin  can. 

Materials:  Lard,  sodium  hydroxide  (caustic  soda), 
salt. 

To  85  cubic  centimeters  of  water  in  the  tin  can  add 
15  grams  of  sodium  hydroxide  and  40  grams  of  lard ;  boil 
slowly  ten  minutes.  Be  very  careful  that  the  mixture 
does  not  spatter  upon  you.  After  boiling  add  about  25 
grams  of  salt  and  continue  to  boil  for  five  minutes.  Then 
allow  all  to  cool  and  remove  the  soap  which  will  be  on 
top.  Let  the  cake  dry  for  several  days,  and  then  see  if 
it  will  produce  suds. 

78.     Bread  Making. 

There  are  several  kinds  of  bread  but  they  can  all  be 
placed  in  two  classes — bread  raised  by  baking  soda  and 
bread  raised  by  yeast.  In  all  cases  the  bubbles  are 
formed  by  carbon  dioxide.  In  Experiment  48,  (d),  we 
saw  that  baking  soda  and  cream  of  tartar,  when  mixed  in 
solution,  produce  carbon  dioxide.  The  cream  of  tartar 
should  be  mixed  dry  with  the  flour,  and  the  baking  soda 
dissolved  in  a  little  water,  if  they  are  to  accomplish  the 
most  good.  Why?  In  Experiment  63  it  was  shown 
that  baking  soda,  when  added  to  sour  milk,  makes  it 
sweet.  At  the  same  time  carbon  dioxide  is  produced  by 
the  action  of  the  acid  in.  the  milk  upon  the  baking-  soda. 


190  THE  ARTS  AND  INDUSTRIES 

This  explains  why  sour  milk  can  be  used  with  soda  for 
pancakes  or  griddle  cakes.  Should  the  baking  soda  be 
added  to  the  milk  or  should  it  be  dissolved  in  a  little  water 
and  added  to  the  mixture  after  the  sour  milk  has  been 
stirred  in?  Explain. 

When  bread  is  made  yeast  is  added  to  make  it  "rise." 
The  yeast  uses  the  sugar  which  is  added  to  the  mixture, 
and  some  of  the  flour  is  changed  to  a  kind  of  sugar  which 
the  yeasts  can  use.  Carbon  dioxide  is  produced  which 
forms  the  bubbles  and  thus  the  dough  swells  and  becomes 
porous  and  tender.  Most  of  the  alcohol  bakes  out.  Why 
is  bread  made  with  warm  water  during  the  cold  weather? 
Another  use  for  yeast  is  in  the  making  of  homemade 
root  beer.  The  stopples  "pop"  when  the  bottles  are 
opened  on  account  of  the  large  amount  of  carbon  dioxide 
which  the  liquid  contains. 

79.     Alcohol  for  Industrial  Purposes. 

Alcohol  may  be  made  from  any  vegetables  or  stalks 
of  crops,  which  contain  starch  or  sugar,  by  means  of 
yeast.  This  means  that  much  of  the  waste  in  crops  due 
to  small  vegetables  or  some  damage  which  renders  the 
vegetables  unfit  for  sale  may  be  turned  into  alcohol 
which  is  very  valuable  for  many  of  the  arts  and  indus- 
tries. Alcohol  is  used  in  large  quantities  as  a  solvent, 
and  it  is  also  used  for  lighting,  heating,  cooking,  and 
for  running  engines. 

The  United  States  Government  has  removed  the  tax 
on  alcohol  if  it  is  not  to  be  used  as  a  drug  or  drink.  The 
only  requirement  is  that  something  must  be  added  to  the 
alcohol  which  will  render  it  unfit  for  persons.  Alcohol 
in  this  condition  is  called  denatured. 


ALCOHOL  FOR  INDUSTRIAL  PURPUOSES 


191 


Experiment  79. — Making  and  Distilling  Alcohol. 
Apparatus:     Burner,  ring  stand,  wire    gauze,    flask, 
tin  grater,  glass  tube,  test  tube,  glass. 

Materials:     Molasses,  potatoes,  yeast. 

a.  Experiment  62  may    be  repeated    and    the    fer- 
mentation  allowed    to    continue 

for  three  days.  Then  arrange 
apparatus  as  shown  in  the  il- 
lustration and  warm  the  mixture 
very  gently.  Alcohol  will  pass 
off  just  before  the  boiling  tem- 
perature of  the  water  is  reached 
and  will  collect  in  the  tube  which 
is  placed  in  the  cold  water.  The 
alcohol  should  b  ur  n  when 
poured  upon  a  plate  and  touched 
with  a  match. 

b.  Grate  some  raw  potatoes,  mix    with  water,    and 
add  about  one-tenth  as  much  yeast    as  there    is    mash 
Allow  to  ferment  as  in  (a)  above,  and  distil. 

80.     The  Pantagraph. 

The  pantagraph,  as  shown  in    the    illustration    is    a 

______          .         -^My.:    r>~ 


192  THE  ARTS  AND  INDUSTRIES 

practical  application  of  the  lever,  and  is  used  to  enlarge 
drawings  or  to  make  them  smaller.  It  is  made  from  four 
long,  thin  sticks  which  have  holes,  at  regular  intervals, 
in  which  pegs  may  be  inserted.  The  block  on  the  right 
hand  lower  corner  is  fixed  to  the  table.  All  the  rest  of 
the  pantagraph  is  free  to  move.  The  point  under 
the  hand  does  not  mark ;  the  point  over  the  smaller  pic- 
ture is  a  pencil.  The  little  wheel  at  the  left  of  the 
pantagraph  is  not  necessary  but  allows  it  to  move  more 
freely.  By  moving  the  point  over  all  the  lines  in  a 
drawing  an  exact  copy  is  made  by  the  pencil  only  the 
new  drawing  is  smaller  in  this  case.  To  enlarge  a  draw- 
ing the  non-marking  point  is  placed  where  the  smaller 
picture  is,  and  the  pencil  is  placed  where  the  hand  in  the 
picture  now  is. 

When  studying  the  lever  you  learned  that  the  small 
force  moves  a  longer  distance  than  the  large  force.  The 
pantagraph  may  be  considered  as  four  levers  all  acting 
together.  A  certain  motion  of  one  part  will  make  a 
larger  or  smaller  motion  of  another  part  according  as 
the  lengths  of  the  arm  are  changed  by  changing  the  pegs. 
Make  a  pantagraph  and  copy  some  drawings. 

81.     Levelling. 

It  is  very  often  desirable  to  know  how  to  make  level 
the  foundations  of  a  building.  The  illustration  shows  a 
very  simple  method  which  has  been  used  for  many  years. 
The  apparatus  is  made  of  the  size  as  shown.  The  plumb- 
bob  hangs  from  (b),  and  the  plumb-line  is  kept  from 
swinging  too  much  by  some  wide  staples.  To  adjust 
the  apparatus  rest  the  two  ends  upon  two  stakes  driven 


LEVELLING 


193 


into  the  ground,  driving  in  the  high  stake  until  the 
plumb-line  is  about  in,  the  middle  of  the  board  (bd). 
Then  mark  just  where  the  point  of  the  plumb  bob  comes 
Reverse  the  apparatus  upon  the  stakes,  without  chang- 
ing them  and  mark  where  the  point  of  the  plumb-bob 
comes.  Exactly  halfway  between  the  two  marks  is  the 
proper  place  to  put  the  level  mark.  When  the  apparatus 
is  placed  so  that  the  plumb-bob  comes  to  this  mark  the 
bottom  stick  is  level. 

Sometimes  a  certain  slant  is  wanted,  as  when  ditches 
are  being  dug  to  carry  water.  In  this  case  a  block  is 
placed  at  (ce),  having  a  length  according  to  whatever 
drop,  as  it  is  called,  is  wanted  for  each  eleven  feet.  Then 
the  apparatus  is  used  as  in  levelling,  but  instead  of  being 
level  the  ground  has  the  slant  which  is  desired. 

Cut  supplied  through  United  States   Department  of  Agriculture. 

Elern.  Sci.   13 


ire  GUIDE 


APPENDIX. 

REFERENCE  BOOKS  ON  BIRDS. 

Farmers'  Bulletins: 

No.     54.     Some  Common  Birds. 
No.  493.     The  English  Sparrow  as  a  Pest. 
No.  506.     Food  of  Some  Well-known  Birds. 
No.  513.     Fifty     Common     Birds     of     Farm     and 
Orchard. 


Finley,  W.  L.,  American  Birds,  Scribners. 
National  Geographic  Magazine,  June,  1913. 

REFERENCE  BOOKS  ON  FLOWERS. 
Farmers'  Bulletins : 

No.     28.     Weeds ;  and  How  to  Kill  Them. 
No.     86.     Thirty  Poisonous  Plants. 
No.  188.     Weeds  Used  in  Medicine. 
No.   195.     Annual  Flowering  Plants. 


Going,  M.,  Field,   Forest,    and    Wayside    Flowers, 
Baker  and  Taylor  Co. 

REFERENCE  BOOKS  ON  TREES. 

Farmers'  Bulletins: 

No.   134.     Tree  Planting  on  Rural  School  Grounds. 
No.   173.     Primer  of  Forestry.     Part  1. 
No.  358.     Primer  of  Forestry.     Part  2. 
No.  423.     Forest  Nurseries  for  Schools. 


Mathews,  F.  S..  Familiar  Trees,  Appletons. 


LIST  OF  APPARATUS  AND  MATERIALS. 


The  numbers  indicate  the  first  experiments  in  which 
the  apparatus  or  the  material  is  used.  The  amount 
needed  will  depend  upon  the  number  of  pupils  but,  as 
will  be  seen,  the  expense  will  be  slight. 


1.  Sticks,  3'x^"x^".  16. 
String.                                      17. 

2.  Rules,  12"— 30cm. 
Scissors. 
Dividers. 

Cardboard.  18. 

Paper  rivets.  19. 

Pins. 

3.  Nails,   assorted. 
Odd  pieces  of  board. 

5.     Protractors. 

Hatpins. 
8.     Bottles,  assorted. 

Files,  triangular. 

Cork  stoppers. 

Glass  tubing,  J4". 

Sand.  20. 

10.  Thumb   tacks. 
Chalk  boxes. 

11.  Window  glass.  22. 
Candles. 

12.  Knives.  23. 

13.  Colored  cloth,     as- 

sorted. 24. 

14.  Blue-print  paper. 


Library  paste. 
Mirrors,  2"x4". 
Rubber  bands. 
Block     of    wood. 

2"x2"x4". 
Drinking  glasses. 
Kerosene  lamp. 
Kerosene. 
Bunsen  burners. 
Alcohol  lamps. 
Alcohol. 
Test   tubes,    6"x24"; 

8"xl". 

Test-tube  holders. 
Iron  Wire,  No.  28. 
Soft  coal. 
Some  article     with 

luminous  paint    on 

it. 

Spice  cans. 
Paper,  asorted  colors. 
Glass  lenses,3"  diam. 
Iron  wire  No.  18. 
Argand  or  student 

lamp  chimneys. 


LIST  OF  APPARATUS 

25.  Unequal       expansion 

apparatus. 
Salt. 

26.  Cheap  thermometers. 

27.  Ring    stands     with 

three  rings. 
Wire  gauze,  5"x5". 

27.  Circular  tin  cans,  as- 

sorted. 

28.  Blocks    of    wood, 

2"x4"x6". 
Wooden     rods,    7" 

long,  1"  diam. 
Lubricating  oil. 

29.  Friction   gaslighters. 

30.  Turpentine. 

Pieces    of    broken 
chinaware. 

31.  Charcoal. 

Pieces      o  f     various 
combustibles. 

33.  Baking  soda. 
Bandages. 
Limewater. 
Olive  oil. 

34.  Copper  rods,  No.  12, 

6"  long. 

Iron  rods,  No.  12,  6 
long. 

37.  Wing  tops  for  Bun 

sen  burners. 

38.  Saucers    o  r    shallow 

dishes. 


AND  MATERIALS  197 

39.  One  20-oz.  bottle. 
Medicine  droppers. 
Phenolphthalein, 

KOZ. 

40.  Potassium  chlorate. 
Manganese  dioxide. 

41.  Glass  funnels. 
Syringe  bulbs. 
Glass  jar,  6"x8". 

Rubber  tubing. 
3-16"  hole. 

42.  Gallon  bottle. 
Large  pan     to     hold 

two  gallons. 

43.  Pie  tins. 

Small   round    bottles 

with  stoppers. 
Levels,  ($.20). 

45.  Balances,     (can     be 

made). 

Set  of  weights,  500  g. 
Sponges. 
-  Stones. 
Pieces  of  bricks. 

46.  Paraffin. 

47.  Filter  paper,  5". 
Sawdust. 

48.  Tin  spoons. 
Sugar. 

Cream  of  tartar. 
Ammonium  chloride. 


198 


APPENDIX 


49.  Gasolene. 
Lard. 
Rosin. 

Pitch,    or   some    tree 
gum. 

50.  Beakers,  200  cc. 
Alum. 

Copper  suphate. 

51.  Powdered  or  shaved 

soap. 

52.  Beans. 

53.  Very    small     glass 

tubing,  assorted. 
Lamp  wicks. 
Red  ink. 
Cube  sugar. 

54.  Cake  pans. 
Gravel. 
Loam. 
Cheese  cloth. 

56.  Blotting  paper. 
Seeds  of   beet,    corn, 

pea,  etc. 

57.  Wooden  tray, 

12"xl2"x2". 

58.  Large  pickle  bottles. 
Black  cloth. 

59.  Paper  in  sheets 

17"xll". 

60.  Labels. 


61.  Seeds  of  apple,  pear, 

orange,  lemon. 

62.  Molasses. 
Yeast. 

63.  Powdered  borax. 
Absorbent  cotton. 

64.  Graduate,  50  cc. 

65.  Materials  etc.  for  bal- 

ance. 
69.     Spring      balances, 

250g.— 8  oz. 
Window  roller 

springs. 

71.  Triangular  pieces   of 

wood. 

72.  Little  car  for  inclined 

plane. 

73.  Lodestone. 
Bar  magnets. 
Horseshoe  magnets. 

74.  Pepper  boxes. 
Iron  filings. 

Section  70. 

Potassium   ferricyan- 

ide,  1  oz. 
Iron-ammonia  citrate 

iy2  oz. 
Gum  Arabic,  %  oz. 

78.  Sodium  hydroxide. 

79.  Tin  vegetable  grater. 
Potatoes. 


OTHER  BOOKS  BY  THE  SAME  AUTHOR 


General  Science  Outline.  Published 
by  Cunningham,  Curtiss,  and 
Welch.  (Out  of  print.) 

Introduction  to  General  Science,  with 
Experiments.  A  text  tor  the  first 
year  of  high  school.  Published 
by  the  Macmillan  Company 

Outline  of  Science  for  the  Fifth 
Grade.  Published  by  Percy  n.. 
Rowell,  Berkeley,  California 

Outline  of  Science  for  the  Sixth 
Grade.  Published  by  Percy  E. 
Rowell,  Berkeley,  California 

Outline  of  Science  for  the  Fifth  and 
Sixth  Grades.  Published  ^  by- 
Percy  E.  Rowell,  Berkeley,  Cali- 
fornia 

Outline  of  Science  for  the  Seventh 
Grade.  Published  by  Percy  E. 
Rowell,  Berkeley,  California 

Outline  of  Science  for  the  Eighth 
Grade.  Published  by  Percy  E. 
Rowell,  Berkeley,  California 

Outlines  of  Science  for  the  Seventh 
and  Eighth  Grades.  Published 
by  Percy  E.  Rowell,  Berkeley. 
California 

Outline     of     Science  for     the     Four 

Upper     Grades,  Published     by 

Percy   E.   Rowell,  Berkeley,    Cali- 
fornia 

Elementary  General  Science.  Book  I 
A  text  based  upon  the  Outline  of 
Science  for  the  F:ith  Grade.  Pub- 
lished by  Percy  E.  Rowell,  Berke- 
ley, California.  Illustrated. 

Elementary  General  Science.  Book  II 
(In  preparation.) 

Elementary  General  Science.  Book  III 
(In  preparation.) 

Elementary  General  Science.  Book  IV 
(In  preparation.) 


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